Sergius Paulus was the proconsul of Cyprus, he became a believer when Paul and Barnabas explained the word of God and then performed a miracle. Acts 13v4–12

Aquila and his wife Priscilla were Christians form Roman who became close friends and helpers of Paul, but the books of Acts does not tell us about them becoming Christians. Acts 18v1–3

Lydia was a worshiper of God when Paul arrived in Philippi.  God opened her heart when Paul spoke and she was baptised a believer.Acts 16v11–15

Stephanas was one of the first believers in Achaia, but we know this from Paul’s first letter to the church in Corinth, he is not mentioned in Acts. 1Corinthians 16v15–18

Simon practiced magic in Samaria, but turned away from it when he became a believer and was baptised after hearing Philip.  But he wanted the power of the Holy Spirit to glorify him not God so he received a stern warning from Peter. Acts 8v9–24

Gaius was baptised by Paul in Corinth.  Paul mentions this fact in his first letter to that church, it is not in the book of Acts. 1Corinthians 1v14

Crispus was an official at the Jewish synagogue in Corinth, but he and his family became Christians when they heard Paul preach. Acts 18v8

Paul (when he was called Saul) famously became a believer through a very dramatic conversion while he was on the road to Damascus. Acts 9v1–22

The Ethiopian Official became a Christian while on a journey.  Philip explained the scriptures to him while he traveled home from Jerusalem. Acts 8v26–40

Damaris was a woman of Athens who became a believer when Paul preached about the resurrection of the dead. Act 17v32–34

Cornelius was a Roman Centurion—he was a gentile, not a Jew.  Peter had to receive a vision from God before he understood that he could spread the good news to non-Jews. Acts Chapter 10

There are two James's in Acts.  The first mentioned is James the disciple, the second James the brother of Christ. But the book does not tell us the story of them becoming Christians. Acts 12v1–3

Epaenetus was the first convert in Asia, but we know this from Paul's letter to the Romans, not from the book of Acts. Romans 16v5

Timothy was an evangelist with Paul and a church leader, but he was already a follower of Christ when Paul met him. Acts 16v1

The Philippian Jailer's life was saved in twice by Paul and Silas.  The first time they stopped him killing himself when God had freed them from the Jail.  The second time was when they explained the Gospel to him and his eternal life was saved. Acts 16v25–34

Dionysius was a member of the government in Athens, he was one of only a few to believe in Christ when Paul preached in Athens. Acts 17v34