Identity-based key agreement protocols allow the participants in a group exchange information over an open network with each other. However, in most of proposed IDbased protocol, identities of group users are exposed, so that eavesdroppers can easily learn who belongs to the specific group. In this paper, we proposed a complete anonymous group key agreement protocol based on the Burmester and Desmedt mechanism and ID-based encryption cryptosystems. The proposed protocol is provably-secure in the random oracle model, and achieves the following security attribute: complete anonymity, unlinkability, group key secrecy, perfect forward secrecy for the group session key and entity authentication.