Mobile ad hoc networks consist of mobile nodes that communicate with one another through radio communication channel. As MANETs are dynamic nature, mobile nodes enters and leaves the MANETs region at any time so there is possibility that the malicious nodes may also involve in the communication process. So MANETs need a security mechanism to have secure communication from attackers as they are vulnerable to security attacks. Different security mechanisms have been designed to solve the security issues via cryptographic techniques. However, these security mechanisms should not have much overhead on network, particularly in constrained resource environment such as Mobile Ad hoc Networks. This work compares the performance overhead of cryptographic techniques such as Chaotic Maps based & RSA based key agreement in MANETs environment. Performance results shows that RSA is considered to be most used in cryptographic techniques but its overhead of time complexity is greater than the Chaotic Maps based cryptography technique. This overhead greatly impact on end to end delay in intended communication. However, Chaotic Maps based cryptography technique is well alternative to RSA with better performance in terms of minimum computational load and lesser key generation time.