The main constraint in message transmission is security. The key must be shared among users so that the authors have a secure transmission in group based message transmission. In this paper they discuss an important security problem that happens in mobile ad hoc network for key agreement in dynamic group. For a communication to be secure, a group key must be shared by all the members of the group. The key must be updated when any member of the group leaves existing group or become a new member of the existing group.