We used a 61-channel electrode array to investigate the spatiotemporal dynamics of electroencephalographic (EEG) activity related to behavioral transitions in rhythmic sensorimotor coordination. Subjects were instructed to maintain a 1:1 relationship between repeated right index finger flexion and a series of periodically delivered tones (metronome) in a syncopated (anti-phase) fashion. Systematic increases in stimulus presentation rate are known to induce a spontaneous switch in behavior from syncopation to synchronization (in-phase coordination). We show that this transition is accompanied by a large-scale reorganization of cortical activity manifested in the spatial distributions of EEG power at the coordination frequency. Significant decreases in power were observed at electrode locations over left central and anterior parietal areas, most likely reflecting reduced activation of left primary sensorimotor cortex. A second condition in which subjects were instructed to synchronize with the metronome controlled for the effects of movement frequency, since synchronization is known to remain stable across a wide range of frequencies. Different, smaller spatial differences were observed between topographic patterns associated with synchronization at low versus high stimulus rates. Our results demonstrate qualitative changes in the spatial dynamics of human brain electrical activity associated with a transition in the timing of sensorimotor coordination and suggest that maintenance of a more difficult anti-phase timing relation is associated with greater activation of primary sensorimotor areas.