This paper proposes a secure session key exchange and mutual authentication scheme between mobile machines in WLAN-based ad hoc networks. One of the main security challenges for secure machine to machine communication is to accomplish a simple and efficient session key exchange and mutual authentication. The main idea of this paper is that non-interactive session key exchange uses the mobile machine's ID and mutual authentication without communication with an authentication server whenever a data transmission occurs between the mobile machines. The proposed scheme is secure against man-in-the-middle attack, impersonation attack, and modification attack.