It depends on what you mean by “believe.” The Bible says that even the devil and his demons believe in Jesus Christ. Belief in His existence must be followed by belief in the saving power of His blood. Then, there must be faith that if you call on Him, He will hear your prayer and will forgive you of your sins. Finally, that belief and faith must be followed by the action of surrendering yourself to Him.
If you believe in Jesus Christ, but have not taken that final step to begin a personal relationship with Him, don’t wait a moment longer. Ask Jesus to forgive you of your sins, truly repent and surrender your will to His. At that moment, your belief will be turned into salvation and the Holy Spirit will come to live inside you. Be sure to read the other answers to the questions on salvation in this FAQs section, especially, “How do I become saved.”