Over the past decade, cyber-attack events on the electricity grid are on the rise and have proven to result in severe consequences in grid operation. These attacks are becoming more intelligent and can bypass existing protection protocols, resulting in economic losses due to system operating in a falsified and non-optimal condition over a prolonged period. Hence, it is crucial to develop defense tools to detect and mitigate the attack to minimize the cost of malicious operation. This paper aims to develop a novel command verification strategy to detect and mitigate False Data Injection Attacks (FDIAs) targeting the system centralized Economic Dispatch (ED) control signals. Firstly, we describe the ED problem in Singapore's deregulated market. We then perform a risk assessment and formulate two FDIA vectors - Man in the Middle (MITM) and Stealth attack on the ED control process. Subsequently, we propose a novel verification technique based on Multi-Agent System (MAS) to validate the control commands. This algorithm has been tested on the IEEE 6-Bus 3-generator test system, and experimental results verified that the proposed algorithm can detect and mitigate the FDIA vectors. © 2021 IEEE.