Secure neighbor discovery is fundamental to mobile ad hoc networks (MANETs) deployed in hostile environments and refers to the process in which two neighboring nodes exchange messages to discover and authenticate each other. It is vulnerable to the jamming attack in which the adversary intentionally sends radio signals to prevent neighboring nodes from exchanging messages. Anti-jamming communications often rely on spread-spectrum techniques which depend on a spreading code common to the communicating parties but unknown to the jammer. The spread code is, however, impossible to establish before the communicating parties successfully discover each other. While several elegant approaches have been recently proposed to break this circular dependency, the unique features of neighbor discovery in MANETs make them not directly applicable. In this paper, we propose JR-SND, a jammingresilient secure neighbor discovery scheme for MANETs based on Direct Sequence Spread Spectrum and random spread-code pre-distribution. JR-SND enables neighboring nodes to securely discover each other with overwhelming probability despite the presence of omnipresent jammers. Detailed theoretical and simulation results confirm the efficacy and efficiency of JRSND.