In this paper, the impacts of mobility on the performance of angle of arrival (AoA) based physical layer secret key (PLSK) is investigated. Specifically, security probability (SP) and consistency probability (CP) are derived to describe the effects of mobility. Moreover, effective key generation rate (EKGR) is defined to evaluate more comprehensively and accurately how the speed in mobile scenario affects the PLSK. The simulation results presented prove the correctness and effectiveness of the analysis, which is important to provide a framework for parameters setting in AoA based PLSK.