The relativistic effects on nonstationary Karpman–Washimi ponderomotive magnetization are investigated in relativistic electron plasmas. The magnetization M p and radiation power [Formula: see text] are obtained as functions of the relativistic parameter α, scaled wave frequency [Formula: see text], and wave number [Formula: see text]. It is shown that the ponderomotive force is more likely to induce a low-frequency and small-scale magnetic field. In addition, the results indicate that the magnetization and radiation power are suppressed by the relativistic effects in the ultrarelativistic case but enhanced in the moderately and weakly relativistic cases, especially in the moderately relativistic regime.