Mobile ad hoc network (MANET) provides an alternative for military applications and disaster response scenarios where fixed networking infrastructure may not be available, but it faces significantly more security considerations than wired network due to its lack of physical infrastructures or centralized authorities. So it poses a number of security challenges to a protocol designer. The main contribution of this paper is a certificateless threshold signature scheme without a trusted party based on the difficulty of solving the computational bilinear Diffie-Hellman problem. Comparing to most of the presented schemes, nodes of our scheme cooperate to generate the master key to eliminate any form of trusted third party and do not need to use any certificate to guarantee the authenticity of the public key. The proposed signature scheme overcomes the inherent key escrow problem of the ID-based public key cryptography (ID-PKC) while avoiding the complicated certificates management of the public key infrastructure (PKI). Moreover, it is provably secure.