The absorption properties of molecules NOx onto C6N8 monolayer were researched thoroughly with density functional theory (DFT) calculations. Detailed MEP, FMO, and reactivity analysis on C6N8 cluster have shown that NO2 and NO were successfully adsorbed onto the C6N8 monolayer with considerable amount of adsorption energy and charge transfer. The electric conductivity of the C6N8 monolayer significantly increased due to the adsorption of the NO2 and NO, resulting in the semiconducting behavior of the material being turned into conducting behavior. It has been established that the absorption rate of NO2 and NO onto the C6N8 nano-cluster is moderate, making their desorption fairly simple, indicating potential in terms of C6N8 sensor's reusability. Hence, C6N8 monolayer could be a promising candidate for sensing NO and NO2, which can be validated through further experimental studies.