Background: This great pandemic of COVID-19 has been a unique stressor that affected all communities in 2020. This study aims to examine the prevalence of anxiety and depression due to the COVID-19 pandemic in Saudi Arabia and to study the emotional cognition scale in the Kingdom of Saudi Arabia (KSA) in relation to the COVID-19 pandemic. Methodology: A descriptive cross-sectional study was conducted on 857 inhabitants randomly selected from the 13 administrative regions of Saudi Arabia, using a validated self-administrated questionnaire comprising six sections. The collected data were summarized and analyzed. Results: Among the majority of the studied participants, 377 (44.0%) were aged from 35 to less than 50 y. There were 489 (57.1%) females and 368 (42.9%) males, 616 (71.9%) Saudi nationals, 715 (83.4%) university-educated or postgraduate, 619 (72.2%) unmarried and 238 (27.8%) married, and 663 (77.4%) living in areas under partial lockdown. The resultant elevated total depression score was statistically significant (p<0.05) for the following: participants younger than 35y, females, Saudis, those with lower education levels, those who were married, students, those with work suspension during the COVID-19 pandemic, and amongst those who experienced complete lockdown. Among the majority of the studied participants, 355 (41.2%) showed mild depression, and 281(32.6) showed moderate anxiety, and were in the growth zone. In addition, the elevated total anxiety score was statistically significant (p<0.05) amongst the following; younger participants, females, Saudi nationals, those with lower educational levels, those who were unmarried, students, those with telework, and those with no curfew. Conclusion: The adverse mental health effects were more prevalent among particular groups of the population, such as females, adults under 35 years old, students, those with lower educational attainments, and those suffering from chronic illnesses. Anxiety was significantly correlated with depression. The practice of preventive measures, e.g., wearing masks, and social distancing to prevent the spread of COVID-19, may have had psychological benefits during the pandemic. Summary: We assessed the mental health status in Saudi Arabia during the first wave of the COVID-19 pandemic. Mild depression and moderate anxiety were prevalent problems, with many determinants and interrelations. Fear was the most infectious emotion, while happiness was the highest. Keywords: Anxiety; COVID-19; Depression; Emotional contagion scale; Mental health; Preventive measurements.