<b><i>Introduction:</i></b> Social media has played a key role in mediating the communication of information during the COVID-19 pandemic. The way information is shared through social media shapes people’s risk perceptions, which in turn affects their mental health and behaviors. This study aimed to assess social media’s impact on the public’s risk perceptions, mental health, and preventive behaviors during the peak of the COVID-19 pandemic. <b><i>Methods:</i></b> A Web-based survey was developed to assess social media exposure, risk perceptions, mental health, and COVID-19-related preventive behaviors among adults in Saudi Arabia. Multivariate logistic regression analysis was used to identify the association between social media exposure and key measurements. <b><i>Results:</i></b> A total of 1,500 individuals participated in the study; of those, 93.2% of participants reported using social media for COVID-19-related information. Twitter (68.3%) followed by Snapchat (25.1%) were the most used platforms. About 44.4% of participants were highly exposed to social media. High social media exposure was significantly associated with higher risks of anxiety (OR = 1.56, 95% CI: 1.19–2.05) and depression (OR = 1.47, 95% CI: 1.01–2.81) and higher levels of COVID-19 risk perception (OR = 1.43, 95% CI: 1.08–1.89). However, social media has no significant impact on the adoption of preventive behaviors. <b><i>Discussion/Conclusion:</i></b> Our results were consistent with the other international studies that were conducted during the COVID-19 pandemic. The anticipated future increase in social media use urges the need for longitudinal studies to investigate the psychological and behavioral effects of social media during emerging pandemics.