The current study used functional near-infrared spectroscopy (fNIRS) to examine cerebral oxygenation changes in the prefrontal cortex (PFC) associated with dual-task processing before and after motor sequence learning. Participants performed self-initiated sequential finger movements that were 4 and 12 units in length with a visual letter-counting task. After practice, dual-task sequence-4 performance revealed decreased activity in the right dorsolateral PFC, medial PFC, and orbitofrontal cortex. However, dual-task sequence-12 performance revealed increased activity in the right ventrolateral PFC when compared to the left hemisphere. The findings suggest that dual-task interference was reduced following practice for dual-task sequence-4. The results also suggest that increased right hemisphere activation is needed to maintain performance when the primary sequential task (e.g., dual-task sequence-12) has a high level of difficulty.