In lane keeping assistance system and method for an automotive vehicle, a control current (Iout) to be outputted to a motor during an automatic steering mode is detected, a filter is provided for the detected control current to pass only signal components of the detected control current whose frequencies are lower than a predetermined cut-off frequency value (fstr, fstr_low, fstr_mid, fstr_hi) to derive a filtered control current (Iout_lpf), a determination of whether a manual steering intervention to the automatic steering occurs is made according to a magnitude of the filtered control current, and the control current outputted to the motor is reduced toward zero when the manual steering intervention is determined to occur according to a result of determination that the magnitude of the filtered control current (Iout_lpf) is in excess of a predetermined threshold current value (Iout_lpf_th).