The intermolecular potential energy surface of the Ar . NO+ cationic complex has been calculated using ab initio methods : RHF, MP2, MP3, MP4, CCSD, and CCSD(T), using the cc-pVDZ and cc-pVTZ basis sets. An additional surface was calculated at the MP2/cc-pVQZ level. All calculations were performed with a fixed NO+ bond length, but in one set of calculations the effect of variation of the NO+ bond length was studied. Finally, the MP2/cc-pVQZ intermolecular potential energy surface was recalculated by performing a point-by-point correction for basis set superposition error. All of these surfaces were used to extract anharmonic intermolecular vibrational frequencies, in order to compare to previous calculations, and experimental results. Rotational energy levels were also calculated.