MANET is a self configurable, self deployable and infrastructure less network in which nodes are continuously moving and creates dynamic topology. For routing the main protocols using are AODV, OLSR, DSDV, DSR etc. AODV and DSR are reactive protocols, where DSDV and OLSR are proactive protocols. This paper deals with AODV and OLSR protocols. Since the topology is dynamic the attacker presence is more. Many attacks such as black hole, worm hole, grey hole , flooding attack etc can occur among this black hole is the main one. The attacker acts as a black node which will fake the source node showing more attractive path to the destination. As a result the source will forward the data through the black node and it will drop the packets. This paper presents a survey on black hole attack in OLSR and AODV protocols and the corresponding mitigation techniques.