In this letter, we investigate the performance of coherent free-space optical (FSO)-orthogonal frequency division multiplexing (OFDM) systems with multiple receivers over an atmospheric turbulence channel considering the frequency offset effect. In particular, we derive an exact average bit error probability (ABEP) of coherent FSO-OFDM systems in a turbulence-induced fading channel. To mitigate the atmospheric turbulence-induced amplitude fluctuations and phase aberrations, a modal compensation technique is assumed to be employed at the receivers. Numerical results confirm the validity of the derived ABEP expression.