Using functional near infrared spectroscopy (fNIRS), we have been researching the effect of musical attention control training (MACT) on the prefrontal lobe, which is involved in attention control. We detected significant dorsolateral prefrontal cortex (DLPFC) activation during music-based tasks that included “dual task” elements. In this study, to elucidate which musical elements influence DLPFC activation, we focused on the effects of tempo of both handed Rhythmic tapping tasks (RTT), which including “dual task” elements. RTT with 3 different tempos, the easy (E) (slow tempo), intermediate (I) (moderate tempo), and difficult (D) (fast tempo) tasks, were developed. Then, the activation of the DLPFC was measured during each task. Our results detected a significantly stronger DLPFC activation during the (D) task than during the (E) task ( p < 0.01) or the (I) task ( p < 0.01). These results indicate that the difficulty of RTT can be adjusted by altering the tempo. Music-based tasks could be useful for cognitive training programs, even those for poorly motivated people with severe attention deficits through changing the difficulty level by changing the tempo.