Density functional theory calculations are performed to investigate how the incorporation of a C atom into B12N12 fullerene-like nanocluster modifies its catalytic activity towards the reduction of nitric oxide (NO) in the presence of CO molecule. The most stable adsorption configurations, adsorption energies, binding distances and net charge transfers are obtained to understand the impact of NO and CO molecules on the electronic properties of B12N12 and B11N12C nanoclusters. Our results suggest a dimer mechanism for the reduction of NO over both surfaces. First, two NO molecules are attached together to form (NO)2 dimer. Then, (NO)2 is dissociated into N2O molecule and an activated O atom (O*). The O* is then removed by a CO or NO molecule, due to a small activation energy. The results indicate that the C-doping can significantly decrease the activation energies needed for the reduction of NO over B12N12.