Background: COVID-19 is the third pandemic of the 21st century, is highly contagious, and can cause anxiety due to the development of serious physical problems and reduction of quality of life. Anxiety is a psychological state experienced by nearly all humans in life. However, it is considered a mental disorder if it exceeds its moderate level. Therefore, this study aimed to determine the anxiety level, mental health, and their related factor in the population above 18 years old in Qaemshahr County.Methods: This descriptive, correlational study was conducted on 400 individuals in Qaemshahr County. Given the population of this county, convenience sampling was employed to select 40% of the participants from the rural population and 60% from the urban population. The data were collected using a demographic questionnaire (7 items), the Corona Disease Anxiety Scale (CDAS) including somatic (physical) anxiety and psychic (mental) anxiety sections, and the 12-item General Health Questionnaire (GHQ). Descriptive and inferential statistical tests (multiple linear regression analysis, independent sample t-test, one-way ANOVA, and Pearsons test) were used in the SPSS 25 software for data analysis.Results: The mean score of mental health was 22.93±8.9, which accounted for 63.69% of the total score of the questionnaire. The total mean score of anxiety was also 9.46±6.89, which contributed to 31.53% to the total score of the questionnaire. According to the results, physical anxiety per se predicted 31% of the dependent variable (mental health).Conclusion: The results showed a significant negative correlation between mental health and anxiety resulting from COVID-19. In other words, the higher the anxiety level, the lower the level of mental health would be. Anxiety also acted as an underlying variable threatening health. Moreover, the mean score of mental anxiety was higher in married, divorced, and widowed participants than in single ones.