During a mental rotation task of hands, participants mentally rotate their hand into the orientation of the shown hand. These mental movements are subject to the body's biomechanical constraints. In this study, we investigated whether the involvement of motor processes during the mental rotation process, as reflected in mu-power desynchronization, is also influenced by one's movement capabilities. We performed an EEG study and used a delayed response mental rotation task of hands to examine the event-related desynchronization differences between movements that are biomechanically easy and difficult to perform. Our results show an increase in event-related desynchronization of the mu power for biomechanically easy compared to difficult-to-adopt postures. These findings provide further evidence for the notion that motor simulations can only be performed for movements that can already be performed overtly.