Background Autism Spectrum Disorder (ASD) is a high-prevalence neurodevelopmental disorder characterized by communicational, social, and behavioral challenges. Complementary and alternative medicine (CAM) is a group of practices and products that fall outside the realm of conventional medicine practiced worldwide. Traditional CAM is a health practice that comes from a particular culture, such as the use of Zamzam water and black seeds in Saudi Arabia. CAM comprises widely utilized practices in Saudi Arabia for children of various ages and adults. In many cases, CAM is used to treat ASD. The aim of this study is to investigate the perspectives of adults in Saudi Arabia toward CAM for treating ASD. Methods A cross-sectional study was conducted by distributing an online questionnaire to adults in different regions of Saudi Arabia. Results A total of 4,311 adults participated in this study; 66.8% were females and 33.2% were male. Half of the participants reported that they knew about ASD (54.7%). More than half of the participants indicated that CAM—including art therapy (69.0%), physical exercise (67.0%), and limiting the use of electronic (55.4%)—could help in ASD management. Around half of the respondents indicated a belief that traditional treatment cannot help in treating ASD (53.9%). Only 20.0% of the respondents thought that ASD could be entirely treated using CAM therapies. The most common source of knowledge about CAM was social media and the internet (58.6%). Conclusions The majority of participants in this study did not believe that ASD could be treated entirely using CAM. In addition, fewer than half of the participants believed that CAM therapies could improve different aspects of ASD, such as behavioral issues. The study highlighted the need for awareness among residents of Saudi Arabia regarding specific treatments for ASD.