The brain-computer interface (BCI) is a new communication scheme that depends on neither the brain’s normal output nerve pathways nor the muscles. Using a BCI system, one can directly translate brain activities into sequences of control commands for an output device such as a computer application [1,2]. Motor imagery is a mental process by which an individual rehearses or simulates a given action in his/her mind but without actually producing movement; it is assumed to involve similar cortical areas that are activated during actual motor preparation and execution [3]. Motor imagery has been widely used as a major approach in BCI studies [4,5].