Aggregate signature scheme was recently proposed by Boneh, Gentry, Lynn and Shacham, which presented a method for combining n signatures from n different signers on n different messages into one signature. In this paper, we propose an identity-based aggregate signature scheme based on the bilinear pairings. This enhances the efficiency of communication and signature verification process. We show that the security of our scheme is tightly related to the computational Diffie-Hellman assumption in the random oracle model.