This study developed and tested the effectiveness of an app-based cognitive behavioral therapy (CBT) program in alleviating anxiety among adolescents and adults with autism without co-occurring intellectual disability. Thirty participants from 15 to 35 years old were randomly assigned to either the intervention or waitlist control group, and self- and caregiver proxy report questionnaires were administered, accompanied by direct behavior observation before and after the intervention period. There was a significant decrease in anxiety level, an increase in positive affect, and a decline in stereotypic behaviors, hyperactivity, noncompliance, and inappropriate speech in proxy reports for the intervention group, compared to the control group. A significant rise in passive response in the direct observation was also seen in the intervention group.