The authors have investigated the possibility of using a plasma as the nonlinear medium for generating phase-conjugate-reflected electromagnetic waves in the microwave region by almost-degenerate four-wave mixing. The reflected beam can be significantly amplified by the plasma. It was found that the phase conjugate reflection is of significant magnitude if the frequency and the wave vector difference of the signal wave, with respect to the pump waves, resonate with the frequency and the wave vector of the ion acoustic mode of the plasma.