The multicast for Mobile Ad-hoc NETwork (MANET) is more vulnerable to attacks. Very few existing works have concentrated on security mechanisms along with Quality of Service (QoS) for multicasting in MANET. Hence in this paper, the authors propose a QoS based clustering technique for multicast security in MANET. In this technique, the nodes with maximum available bandwidth and residual energy are elected as cluster heads which act as multicast group leaders. Each cluster head computes the trust value of its members using success ratio of data and control packets. Based on the trust value, the cluster head decides whether a node is authorized to join the multicast group or not. When the multicast source wants to transmit the data packet, it utilizes the secret key based packet forwarding technique.