Aggregate signature is very useful in special areas where the signatures on many different messages generated by many different users need to be compressed and required to be verified only once. Certificate-based cryptography reduces the complicated certificate management in traditional public key cryptography, overcomes key escrow problem in identity-based cryptography and eliminates lower credibility of trusted third party (TTP) in certificateless cryptography. Considering the merits of certificate-based cryptography and aggregate signature, this paper proposes an efficient certificate-based aggregate signature (CBAS) scheme. Its security proof was given in the random oracle mode and it could be reduced to Computational Diffie-Hellman problem. The length of aggregated signature is constant and the signature verification only needs four pairings computation, and it is independent of the number of signers; moreover, our scheme does not need a secure channel. Hence, the new scheme has the advantages of low communication cost and less computation, and it is more suitable for the application scenarios with limited communication resources.