Attention to sensory stimulation modulates behavioural responses and cortical activity. Attention to movement can also modulate motor responses. For example, directing attention away from cued movements can increase reaction times. This study used fMRI to determine where in the motor cortex attention to movement modulates activity. Attention to movement was reduced by asking subjects to perform a concurrent distractor task (counting backwards). Sensori-motor areas showing a negative interaction between counting and movement (i.e. reduced activation in the dual task condition relative to the sum of the single task conditions) included the supplementary motor area (SMA), cingulate cortex, insula and post-central gyrus. A separate volumes-of-interest analysis revealed significant reductions in mean percent signal change in the dual task compared to the single task in a portion of the pre-central gyrus, deep in the central sulcus (thought to correspond to area 4p) and SMA. We conclude that the brain network for motor control is modulated by attention at multiple sites, including the primary motor cortex. These results are also discussed with reference to theories concerning the neural correlates of dual task performance and mental calculation and have implications for the interpretation of functional imaging studies of normal and impaired motor performance.