In many secure application scenarios, establishing a temporary group without revealing group member information is difficult but desirable. Secure group communication can significantly reduce the computation and communication overhead. Traditional group key management schemes are based on a hierarchical tree. Any network entity who wants to set up a group needs to know the keys of the other group members, i.e., the group key establishment must be done before starting the group communication. As a result, the group needs the group formation beforehand. In this paper, we propose a secure grouping scheme providing anonymity for group members to outsiders. Our approach is based on Attribute Based Encryption (ABE) schemes. In our scheme, each network entity is assigned with a set of attributes. Each group is identified by a logical combination of attributes, i.e., the group access policies. The presented solution has an advantage that there is no need for any prior knowledge of other group members. Instead, the sender just needs to focus on the group access policies. Our scheme further preserves the group formation policies by using a gradual exposure method on attributes. Compared to existing hidden-policy schemes, our solution can greatly reduce the computation and communication overhead.