Security, anonymity, and scalability are important issues for mobile ad hoc network routing protocols, especially in private-vital practical applications. Although there are several papers on anonymous secure routing in mobile ad hoc networks, few research works can achieve sufficient anonymity and strong security, and at the same time provide good scalability. Therefore, in this paper, we present a new distributed anonymous secure routing protocol with good scalability for mobile ad hoc networks. The proposed protocol addresses the problems of anonymous routing and later anonymous data transmission via a dynamic identity pseudonymity approach based on Incomparable Public Keys. Good scalability is achieved by using Diffie-Hellman key exchange scheme and symmetric key cryptography, instead of public key cryptography. In comparison with other previous anonymous secure routing protocols, the proposed protocol not only has strong security and sufficient anonymity protection, but also provides better scalability.