Magnetization dynamics in a ferromagnet can induce a spin-dependent electric field through a spin motive force. Spin current generated by the spin-dependent electric field can in turn modify the magnetization dynamics through spin-transfer torque. While this feedback effect is usually weak and thus ignored, we predict that in Rashba spin-orbit coupling systems with a large Rashba parameter α(R), the coupling generates the spin-dependent electric field [±(α(R)m(e)/eħ)(z[over ^]×∂m/∂t)], which can be large enough to modify the magnetization dynamics significantly. This effect should be relevant for device applications based on ultrathin magnetic layers with strong Rashba spin-orbit coupling.