A mobile adhoc network is an autonomous network that consists of nodes which communicate with each other with wireless channel. Due to its dynamic nature and mobility of nodes, mobile adhoc networks are more vulnerable to security attack than conventional wired and wireless networks. One of the principal routing protocols AODV used in MANETs. The security of AODV protocol is influence by malicious node attack. In this attack, a malicious node injects a faked route reply claiming to have the shortest and freshest route to the destination. However, when the data packets arrive, the malicious node discards them. To preventing malicious node attack, this paper presents PPN (Prime Product Number) scheme for detection and removal of malicious node.