We report results from 1H and 133Cs nuclear magnetic resonance (NMR) studies on CsAu·NH3. This compound has recently been synthesized and belongs to the family of ammoniates. The intense blue color of the material, which is not observed in the parent compounds, suggests that a charge-transfer electronic state is formed. The 1H NMR line shape and relaxation rates are found to be very similar to the corresponding properties in pure ammonia. However, the 133Cs-NMR properties of CsAu·NH3 strongly deviate from the corresponding ones in CsAu, and we show that the former can be interpreted consistently within a localized charge distribution due to either an anharmonic charge density wave state induced by a charge transfer process or an Anderson localization mechanism.