This is a very important question t ask and answer Biblically.  The reason it is necessary is that there are many out there today who claim to be Apostles.  The Mormon Church for example believes that they have 12 living Apostles to this day.  The New Apostolic Reformation claims to have many apostles.  Also there have been many random people who have bestowed upon themselves the title of Apostle.  How do we discern who an apostle is?

The word Apostle simply means “one who is sent”.  A good way of thinking about it would be like an ambassador or messenger sent by a Nation.  With that understanding we can see that there are two kinds of Apostles in the Bible.

Apostles of Jesus Christ

There are only twelve apostles that fit this definition.  These apostles were commissioned directly by Christ in the flesh and thus are eye witnesses to the Resurrection.

“16 You did not choose me, but I chose you and appointed you that you should go and bear fruit and that your fruit should abide, so that whatever you ask the Father in my name, he may give it to you.” John 15:16 ESV

“15 But the Lord said to him, “Go, for he [Paul] is a chosen instrument of mine to carry my name before the Gentiles and kings and the children of Israel.  16 For I will show him how much he must suffer for the sake of my name.” Acts 9:15-16 ESV

“27 Now you are the body of Christ and individually members of it.  28 And God has appointed in the church first apostles, second prophets, third teachers, then miracles, then gifts of healing, helping, administrating, and various kinds of tongues.” 1 Cor 12:27-28 ESV

“11 And he gave the apostles, the prophets, the evangelists, the shepherds and teachers,  12 to equip the saints for the work of ministry, for building up the body of Christ” Eph 4:11-12 ESV

“13 And he went up on the mountain and called to him those whom he desired, and they came to him.” Mark 3:13 ESV

“6 So when they had come together, they asked him, “Lord, will you at this time restore the kingdom to Israel?” 7 He said to them, “It is not for you to know times or seasons that the Father has fixed by his own authority. 8 But you will receive power when the Holy Spirit has come upon you, and you will be my witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth.” Acts 1:6-8 ESV

Are the Apostles still witnesses to the ends of the earth?  Yes they are, they simply teach us in the New Testament now instead of in person.  We have this promise from Jesus in the Gospel of John.

“26 But the Helper, the Holy Spirit, whom the Father will send in my name, he will teach you all things and bring to your remembrance all that I have said to you.” John 14:26 ESV

Many today try to use the above verse to argue that the Holy Spirit reveals all truth to use individually when we ask in prayer.  This promise in scripture is not for us though, notice Jesus is speaking directly to the Apostles.  So we know from scripture that all truth is promised to them.  Therefore we would expect that which God intended for us to know of that truth to be found in the New Testament.

Those sent by the Apostles

Another group of Apostles in scripture are those sent by the apostles directly.  They seemed to have qualifications for whom they chose.

“21 So one of the men who have accompanied us during all the time that the Lord Jesus went in and out among us, 22 beginning from the baptism of John until the day when he was taken up from us—one of these men must become with us a witness to his resurrection.” 23 And they put forward two, Joseph called Barsabbas, who was also called Justus, and Matthias. 24 And they prayed and said, “You, Lord, who know the hearts of all, show which one of these two you have chosen 25 to take the place in this ministry and apostleship from which Judas turned aside to go to his own place.” 26 And they cast lots for them, and the lot fell on Matthias, and he was numbered with the eleven apostles.” Acts 1:21-26 ESV

Did God choose Matthias through the casting of the lot above?  This I don’t know.  I personally find the notion unlikely as the text doesn’t directly say.  But what I do see is that qualifications are cited that the Apostles used to ordain and send out:

• They had accompanied them during Christ Ministry
• They had witnessed the Resurrection

This second group of “apostle” is referred to in scripture as “messengers of the churches”(2Cor 8:23).  Instead of being sent by Christ in the flesh they were sent out by an Apostle who was.  Grace to You, a Ministry by John MacArthur has an excellent article that addresses the two classes of Apostles you can find HERE.  Below is an excerpt:

“The term apostle is used in a more general sense of other men in the early church, such as Barnabas (Acts 14:4), Silas and Timothy (1 Thess. 2:6), and a few other outstanding leaders (Rom. 16:7; 2 Cor. 8:23; Phil. 2:25). The false apostles spoken of in 2 Cor. 11:13 no doubt counterfeited this class of apostleship…

…Apostles in both groups were authenticated “by signs and wonders and miracles” (2 Cor. 12:12), but neither group was self–perpetuating. In neither sense is the term apostle used in the book of Acts after 16:4. Nor is there any New Testament record of an apostle in either group being replaced when he died.” – Grace to You

Conclusion

The bottom line is that the qualifications for the Biblical office of Apostle are rather narrow.  At the very least you would need to have lived in the first century to be sent by Christ in the flesh or to have witnessed the Resurrection.  Since there isn’t a soul on this planet who can claim either of those, it follows that if someone is claiming to be an Apostle they are simply lying.