Wireless mesh network (WMN) is a rapid deployed, self organized and multi-hop wireless networks. However, the wireless and distributed natures of WMN make it subject to various kinds of malicious attacks, which raise a great challenge in securing these networks. Most existing security mechanisms are based on cryptographic keys where a high degree key management services are in demand. In this paper, we present an effective secure key management scheme (SKeMS) which seeks an encryption key assignment such that the induced network is securely key connected and well protected against potential malicious eavesdropping attacks. Compared to previous work, our scheme assigns the available encryption keys among all the nodes in the network. Our simulation results show that our scheme outperforms previous schemes through providing a network that is resistant to malicious eavesdropping attack.