To regulate the temporal structure of a series of behavioral sequences involving multiple actions, it is essential to monitor the progress of the entire behavioral process. To identify the involvement of three cortical motor areas in monitoring behavioral sequences, we examined neuronal activity while monkeys sequentially performed a series of motor tasks in accordance with a predetermined behavioral schedule that included a numerical structure. We found that neurons in the pre-supplementary motor area exhibited activity that appeared to monitor the performance of the behavioral trials in a binary-coded manner. One-half of the activity represented odd-numbered trials within a behavioral sequence, whereas the other one-half represented even-numbered trials. Such neuronal activity, resembling the operation of binary counting elements widely used for constructing artificial computing devices, was rare in the supplementary motor area or in the primary motor cortex.