Mobile Ad hoc networks (MANET) are characterized by wireless connectivity, continuous changing topology, distributed operation and ease of deployment. Wireless ad hoc networks are not protected against the attack of malicious nodes, because of security vulnerabilities in the routing protocols. There are many security issues found in MANET due to continuous changing of their topology. The most commonly identified attack is black hole attack which causes the packets being dropped during the transmission. The work proposed in this paper contributes to detect the black hole attack using Modified Associativity Based Routing protocol (MABR) which is the modification and improvement of ABR.