Magnetoelectric (ME) effect refers to the coupling between electric and magnetic fields in a medium resulting in electric polarization induced by magnetic fields and magnetization induced by electric fields [1,2]. The linear ME effect in certain magnetoelectric materials such as multiferroics has been of great interest due to its application in the fabrication of spintronics devices, memories, and magnetic sensors [3-7].However, the exclusive studies on the nonlinear ME effect are mostly centered on the investigation of second-harmonic generation in chiral materials [8][9][10]. Here, we report the demonstration of nonlinear wave mixing of optical electric fields and radiofrequency (rf ) magnetic fields in thermal atomic vapor, which is the consequence of the higher-order nonlinear ME effect in the medium. The experimental results are explained by comparing with density matrix calculations of the system. We also experimentally verify the expected dependence of the generated field amplitudes on the rf field magnitude as evidence of the magnetoelectric effect. This study can open up the possibility for precision rf-magnetometry due to its advantage in terms of larger dynamic range and arbitrary frequency resolution.