The Catechism in Questions & Answers

436. Were there any other Apostles besides these during the beginnings of the church?

Yes. In addition to the twelve, the New Testament also mentions Matthias (cf. Acts 1: 15-26), Barnabas (cf. Acts 13: 1-4; 14: 4, 14), Paul (cf. 1 Corinthians 9: 1-16; 2 Corinthians 11), and James the brother of the Lord (cf. Galatians 1: 19; 2: 9). Silvanus and Timothy are also described as Apostles (1 Thessalonians 1: 1; 2: 7), as are Andronicus and Junia (cf. Romans 16: 7).
It is of note here that only in the case of Matthias was it necessary to have been an eyewitness of Jesus’ activity in order to be called as an Apostle (Acts 1: 21-22).