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The optimal conditions for inducting the appropriate brain activation when rehabilitation robots are used should be clarified for the development of rehabilitation robots based on the concept of brain plasticity. In the current study, we attempted to investigate differences in cortical activation according to the speed of passive hand movements performed by a rehabilitation robotic hand. Nine normal subjects were recruited for this study. Passive movements of the right hand were performed by the rehabilitation robotic hand using three different speeds: 1 Hz (fast), 0.5 Hz (moderate) and 0.25 Hz (slow). We measured values of oxy-haemoglobin (HbO) in four regions of interest: the primary sensory–motor cortex (SM1), supplementary motor area (SMA), premotor cortex (PMC) and prefrontal cortex (PFC). The HbO value in the left SM1 was significantly higher during movements performed at 0.5 Hz than during movements performed at 1 Hz and 0.25 Hz (p< 0.05); in contrast, no significant differences were observed in the left SMA, PMC and PFC (p> 0.05). The results of a group analysis of HbO showed a significant activation in the left SM1, SMA and PFC during movements performed at 0.5 Hz. By contrast, significantly less activation was observed in the left SM1 during movements performed at 1 Hz and 0.25 Hz. This study showed that movements performed at 0.5 Hz by a rehabilitation robotic hand induced the greatest cortical activation in the contralateral SM1. As a result, it appears that hand movements performed at a moderate speed by the rehabilitation robotic hand could induce the greatest cortical activation in the contralateral SM1.