Currently, Network Mobility (NEMO) Basic Support protocol enables the attachment of mobile networks to different points in the Internet. It permits session continuity for all nodes in the mobile network to be reachable as the network moves. While this standard is based on the MobileIPv6 standard, it inherits these disadvantages such as security vulnerabilities. To manage the problems of NEMO, many schemes combine it with a network-based approach such as Proxy Mobile IPv6 (PMIPv6). Despite the fact that this latter expedites the real deployment of IP mobility management; it suffers from lack of security. Therefore, we propose an Efficient and Secure Mutual Authentication Mechanism during initial attachment in NEMObased Proxy Mobile IPv6 Networks called EMA-NEMO based PMIPv6 in order to provide mutual authentication between a mobile router and diameter server during initial attachment of the mobile router to a PMIPv6 domain. Moreover, we evaluate the performance of our scheme using the Automated Validation of Internet Security Protocols and Applications (AVISPA) software which has proved that authentication goals are achieved.