A 26-year-old man with intractable focal motor seizure beginning with tonic contraction of the left orbicularis oculi muscle had prolonged EEG monitoring with subdural grid electrodes placed over the right perirolandic cortex. Electrical stimulation of the cortex with implanted subdural electrodes showed a relatively low threshold for afterdischarges (ADs) but could not disclose the motor area for the left upper face where or near where the epileptogenic area was expected to be present. Bereitschaftspotential recorded from the subdural electrodes in association with self-paced voluntary blink (eyelid closing) disclosed the motor area specifically related to voluntary movements of the left upper face, which was most likely buried in the sulcus. This observation suggests that recording of Bereitschaftspotential from subdural electrodes is useful for mapping the motor cortex, especially in patients with focal motor seizure with low threshold for ADs to electric stimuli.