We report results from H-1 and Cs-133 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 H-1 NMR line shape and relaxation rates are found to be very similar to the corresponding properties in pure ammonia. However, the Cs-133-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.