Ad Hoc networks are characterized by frequently changing network topology. Due to the lack of central authority, forming security association among a group of members in Ad Hoc networks is more challenging than in traditional networks. With the view in mind, group key management plays an important building block of any secure group communication. In this paper, we proposed a group key management based on Identity-based Cryptosystem and Chinese Remainder Theorem. In the proposed scheme, there are no requirements of member serialization and existence of a central entity. Besides this, the scheme the protocol also many highly desirable properties such as contributory and efficient computation of group key, uniform work load for all sensor nodes and efficient support for high dynamics. Compare to other existing group key agreement protocols, the proposed protocol make no assumption about the structure of the underlying wireless network, making it suitable for Ad Hoc networks.