We investigate the influence of electron correlation on NO-adsorbed manganese phthalocyanine (MnPc). A generalized gradient approximation (GGA) calculation determines that the magnetic moment of thecentral Mn atom is quenched by the adsorption of NO. In contrast, the GGA+U method (U> 1.0 eV) and three hybrid functionals predict a high spin polarization of the Mn atom. Further inconsistencies betweenthe GGA approach and the alternative methods have also been found for the geometric structure, theordering of orbitals and orbital occupation. This study suggests that besides the band gap, electron correlation has a strong effect on geometric, electronic and magnetic properties.