This study aimed to examine the relationships among electroencephalogram parameters as physiological indices, ballistic movement as an index of operation, and accuracy of task performance. Experiments were conducted using a "reaching" task, in which subjects touched the target appearing 300 pixels away from a start point in a vertical direction on a touch-sensitive screen with the forefinger. During experiments, EEG, EMG as trigger, high-speed camera images, and task efficiency were acquired. Significant differences between the high- and low-performance groups were clearly confirmed on the slope of NS (negative slope) in movement-related cortical potentials (MRCPs) acquired from Fz (p < 0.05) and Cz (p < 0.05). Furthermore, a difference between these groups was confirmed in duration of ballistic movement. Based on our findings, we discuss whether it is possible to extract MRCP rapidly and automatically without using signal averaging and also to estimate accuracy just before a motion is executed.