Individuals with autism spectrum disorder (ASD) often have difficulty with coordinated fine motor skills, but the degree of difficulty significantly varies from person to person. To elucidate the cause of this diversity, we monitored brain activity during fine movement tasks (tying bowknots) by near-infrared spectroscopy in 17 adults with ASD and 18 adults with typical development matched for age, gender, and intelligence quotient (IQ). We also examined the relationship between brain activation and developmental characteristics, including ASD severity, using the Autism-Spectrum Quotient and the Multi-dimensional Scale for Pervasive Developmental Disorder and Attention-Deficit/Hyperactivity Disorder. Although participants in the ASD group did not show significant clumsiness, their right prefrontal cortexes were relatively less activated, particularly in individuals with poor social skills and inattention. Our study indicates that individuals with ASD traits may use different strategies when performing fine movements; that is, they less use the brain areas responsible for processing visual image or planning behaviors.