Context: Autism spectrum disorder (ASD) is a complex neurological disorder characterized by persistent deficits in communication, impairments in social interactions, and repetitive behaviours (RB). Recently, motor impairments have been documented to be another core characteristic of ASD, which leaves individuals with ASD at risk for health problems due to inactivity, similar to those without disability who are inactive. Thus, involvement in physical activity can benefit those with a diagnosis of ASD. In addition to the health benefits, exercise may help reduce the expression of RB. Reducing RB may assist an individual’s ability to learn skills for daily living. Therefore, the purpose of this study was to examine the effect of aerobic exercise on improving performance on simple motor tasks and reducing RB. Methods: Seven participants with a diagnosis of ASD and an intellectual disability engaged in the Box and Block Test or the Grooved Peg Test on alternate days before and after 20 minutes of aerobic exercise on a stationary bike. The motor tests were performed twice with the right hand and an average score was recorded along with the number of RBs exhibited. Results: Directly following 20 minutes of aerobic exercise, results indicated an average of a 4% improvement in performance in the Box and Block Test, and a 2.3% average improvement in participants’ performance on the Grooved Peg Test. The exercise intervention did not result in an overall decrease in RB. Discussion: While there was modest improvement in the two motor skill tasks, the lack of change in RB may be due to the low number of behaviours exhibited by some of the participants. Consequently, targeting those with more severe forms of RB may provide a more appropriate focus for future studies.