The benzene-argon S-1 intermolecular potential energy surface is evaluated using coupled-cluster linear response methods and an augmented correlation-consistent polarized valence double-zeta basis set extended with midbond functions. As a result of the S-1<-- S-0 excitation, the well depth of the potential increases and the benzene-argon equilibrium distance is decreased by 0.065 Angstrom. Full three-dimensional vibrational calculations of the van der Waals vibrational energy levels, using the ab initio potential, are in good agreement with available experimental data.