CPS is often comprised of several networked systems that could really observe as well as modify real-world objects and operations. They're analogous with IoT systems, and that therefore CPS concentrates mostly on interplay of mechanical, communications, as well as compute operations. As a result of their connection with IoT, a truly innovative CPS element, the “Internet of Cyber-Physical Things (IoCPT)”, has been established. The speedy pace and substantial development of CPS does have a consequence upon several parts of people's lives and permits a plethora of services and applications, including such e-Health, home automation, and e-Commerce. Interlinking the physical and virtual realms, on the other hand, poses additional security risks. As a necessary consequence, CPS cyber-security increasingly piqued the interest of both academics as well as corporations. In this research work, a literature review has been undergone in terms of cyber security in cyber physical systems. All the literature papers on cyber security have been collected from standard journals like IEEE, Springer and Elsevier. The collected papers are analyzed in diverse aspects like application, dataset used, technique utilized, tool and performance recorded. Finally, the research gaps identified is manifested to guide the future researchers on intrusion detection in CPS.