Background: The coronavirus disease (COVID-19) pandemic is an international public health threat. This study aimed to evaluate COVID-19-related knowledge, preventive behaviors, and risk perception among Saudi Arabian medical students and interns. Materials and Methods: This cross-sectional study was conducted among fourth- and fifth-year medical students and interns between June and August 2020 at three colleges of medicine in Qassim Region, Saudi Arabia. A previously validated questionnaire was distributed as an online survey. Results: The total mean knowledge score was 12.5/15 points; 83.9% achieved a high score. The mean score of self-reported preventive behavior was 8.40; 94.1% achieved a high score. The overall mean risk perception score was 5.34/8 points; 31.6% achieved a high score. Conclusion: Medical students assessed in this study displayed sufficient knowledge and preventive behaviors regarding the COVID-19 pandemic and an average level of risk perception. Lower scores by younger medical students suggest that they must improve their COVID-19 knowledge and risk perception, as they are a potential source of health information in their communities.