This Letter reports on the experimental observation of quantum beats stimulated by a resonance radio-frequency field in the recombination luminescence of radical-ion pairs. The beat frequency for solutions of p-terphenyl in squalane increases linearly with rf-field amplitude in the range 1 to 10 G in a rotating frame. The beat frequency corresponds to the theoretically calculated one, with amplitude twice as low as the theoretical one. This is attributed to contributions from the recombination of spin-uncorrelated radical-ion pairs