MANETs are the collection of wireless nodes that can dynamically form a network anytime and anywhere to exchange information without using any pre-existing infrastructure. There are some challenges that make the design of mobile ad hoc network routing protocols a tough task. Firstly, in mobile ad hoc networks, node mobility causes frequent topology changes and network partitions. Secondly, because of the variable and unpredictable capacity of wireless links, packet losses may happen frequently. Moreover, the broadcast nature of wireless medium introduces the hidden terminal and exposed terminal problems. Additionally, mobile nodes have restricted power, computing and bandwidth resources and require effective routing schemes. The highly dynamic nature of MANET coupled with limited bandwidth and battery power imposes severe restrictions on routing protocols especially on achieving the routing stability. Due to all these constraints, designing of a routing protocol is still a challenging task for researchers. In this paper an attempt has been made to evaluate and compare the impact of different mobility models on the performance of three most commonly used on-demands routing protocols named as AODV, DSR and LAR. The performance of these routing protocols has been simulated using QualNet 5.0 simulator.