In this paper, we consider a non-orthogonal multiple access system with imperfect successive interference cancellation and physical layer security where the source node communicates with Users via an energy harvesting relay node. This node uses a power-switching architecture to harvest energy from the sources signals and applies an amplify-and-forward protocol to forward signals. Moreover, the transmit jamming or artificial noise is generated by source node to enhance the security of system in the case an eavesdropper tries to overhear the confidential information from the source. To evaluate the secrecy performance of the proposed system, the asymptotic secrecy outage probability over the Rayleigh fading channel is studied. These results are compared with the secrecy performance of the orthogonal multiple access system and the system without the help of relay. Monte-Carlo results are presented to verify the theoretical results.