Dictionary of Biblical Words:
Although this term only occurs in Acts 5:14; and 1 Timothy, it is perhaps the best general name for those who are saved; expressing, as it does, the principle of salvation—faith, and not being so generally adopted by the unconverted as “Christians.”
Concise Bible Dictionary:
This word occurs but twice in the A. V.
1. πιστεύω, “to believe,” from πίστις, “faith” (Acts 5:14): “Believers were the more added to the Lord.” The same Greek word is constantly used for those that believe on the Lord Jesus Christ to the saving of their souls, as in John 3:15-18.
2. πιστός, “trusting, trusty,”‘ also from πίστις, “faith” (1 Tim. 4:12); “be thou an example of the believers.” The same word is used for “What part hath he that believeth with an infidel, or unbeliever?” (2 Cor. 6:15). “Believers” are a class of persons, who, through the mercy of God, have faith in Christ as the Son of God, and in His atoning work on the cross. See FAITH.