A Mobile Adhoc Network (MANET) is prone to attacks. Adversaries take hold of the network, thus degrading their performance. Various attacks are prevalent in MANET, out of which Byzantine attack plays a vital role. A node or group of nodes present in the routing path between the source and the destination may be compromised due to Byzantine attack. In this paper, Cohen Kappa Reliability Coefficient based Mitigation (CKRCM) mechanism is proposed to deal with these attacks. The intermediate nodes are monitored by their neighbors for a timestamp. If the monitoring node does not receive an acknowledgment, then the nodes are perceived to be attacked. The trustworthiness of the nodes is built by computing the trusts and reliabilities of the nodes. It is seen that the proposed scheme outperforms the existing scheme in terms of Throughput, Packet Delivery Ratio (PDR) and Packet Loss Ratio (PLR).