The simple and short answer to this question is, no. Baptism is not necessary to become a Christian. Of course, baptism is a very important part of the Christian life and all Christians should become baptized. But, baptism is not a requirement for salvation, faith is. In fact, the Bible tells us that we are justified by faith (Rom. 5:1). Justification is the declaration by God upon a sinner that the sinner is righteous in his sight. This is accomplished by faith.
However, the members of the International Church of Christ (ICC) maintain that baptism is a necessary requirement for salvation and that proper baptism must be by immersion in the International Church of Christ. Such a teaching is false and dangerous because it effectively retains the keys to salvation and can use them to control and manipulate their church members. Nevertheless, they quote verses such as John 3:5 (see related paper) and Acts 2:38 (see related paper) as proof of their position. In so doing, they ignore the numerous Scriptures to teach us that salvation is by grace through faith (John 5:24; Acts 13:38-39; Gal. 2:16; 3:26; Rom. 3:24; 4:5; 5:1; 5:9;9:30; 10:10; Eph. 2:8; Phil. 3:9; etc.) For a list of these verse please see the list of verses showing justification by faith.
Another way to make it obvious that baptism is not necessary to be saved, I offer in this illustration. Let's suppose that a person, under the conviction of the Holy Spirit (John 16:8), believed in Jesus as his Savior (Rom. 10:9-10; Titus 2:13), and has received Christ (John 1:12). Is that person saved? Of course he is if you believe the Bible that says we are saved by faith (Eph. 2:8). Let's further suppose that this person who confesses his sinfulness, cries out in repentance to the Lord, and receives Jesus as Savior, then walks across the street to get baptized at a local church. In the middle of the road he gets hit by a car and is killed. Does he go to heaven or hell? If he goes to heaven then baptism isn't necessary for salvation. If He goes to hell, then trusting in Jesus, by faith, isn't enough for salvation. If a person responds that he does not know, then baptism is not necessary for salvation because if it were, then the person would be damned.
A further scriptural demonstration that baptism is not necessary for salvation, we need to take a look at Acts 10:44-48.
"While Peter was still speaking these words, the Holy Spirit fell upon all those who were listening to the message. 45 And all the circumcised believers who had come with Peter were amazed, because the gift of the Holy Spirit had been poured out upon the Gentiles also. 46 For they were hearing them speaking with tongues and exalting God. Then Peter answered, 47 "Surely no one can refuse the water for these to be baptized who have received the Holy Spirit just as we did, can he?" 48 And he ordered them to be baptized in the name of Jesus Christ. Then they asked him to stay on for a few days," (Acts 10:44-48).
Notice that Peter had been preaching the gospel and the Holy Spirit fell upon the people listening. In verse 45 we see that "the gift of the Holy Spirit had been poured out upon the Gentiles also." These people were saved. The gift of the Holy Spirit was on the Gentiles and they were speaking in tongues. This is significant because tongues is a gift given to believers, see 1 Cor. 14:1-5. Also, unbelievers don't praise God. They can't because praise to the true God is a deep spiritual matter that is foreign to the unsaved (1 Cor. 2:14). Therefore, the ones in who are speaking in tongues and praising God are definitely saved and they are saved before they are baptized. This simply isn't an exception. It is a reality. Acts 10:44-48
To say that baptism is a requirement in order to be saved goes against the Scriptures that say that salvation is a free gift (Rom. 6:23) received by faith (Eph. 2:8). Baptism is not necessary for salvation. However, out of obedience to Christ, every Christian should be baptized. To refuse baptism is to be willfully disobedient and sinful.