Securing multicast communications in ad hoc networks must consider several challenging factors such as high nodes mobility, limited bandwidth and constrained energy. Moreover, the establishment of a key management protocol within ad hoc environment meets the "1 affects n" problem, which is more critical in such type of networks, due to the high dynamicity of groups. In this papers, we present an efficient clustering scheme for multicast key distribution in Mobile ad hoc networks. This scheme divides the multicast group into clusters, according to the localization of the group members and their mobility. Simulations indicate a valuable reduction in the average latency of keys distribution and a promising reduction in energy consumption. Analysis also shows that our scheme is scalable.