A group key agreement protocol allows participants to cooperatively establish a common session key which is used to encrypt or decrypt transmitted messages among them over an open network environment. In this paper we propose a secure group key agreement protocol based on the self-certified signature scheme which is suitable for the mobile ad hoc network environment. Under the DDH assumption, the proposed protocol is demonstrated to be secure against passive adversaries. Under the random oracle model and DL assumption, the proposed protocol is demonstrated to be secure against active adversaries. Besides, our protocol provides forward secrecy and withstands known-key attacks.