Background There is evidence that patients with COVID-19 have a higher prevalence of mental health problems than the normal population. This study aimed to investigate the prevalence of mental health problems and their associated factors in patients with asymptomatic or mildly symptomatic in the hospitel in Thailand. Methods Mental health problems were evaluated using the Depression, Anxiety, and Stress Scale - 21 items, and Patient Health Questionnaire-9. The prevalence of mental health problems was presented by frequency and percentage. McNemar's test was used to compare the prevalence of mental health problems between day 1 and day 7. Binary logistic regression was used to identify potential predictors of mental health problems. Results A total of 186 participants (68.3% female; mean age = 37.21 years (SD 13.66) were recruited. The depression, anxiety, and stress rate on day 1 of admission was 26.9%, 32.3% and 25.8%, respectively. Having mild COVID-19 symptoms was a significantly associated factor with anxiety (OR=2.69, 95%CI: 1.05-6.89) and stress (OR=4.53, 95%CI: 1.32-15.55). Conclusions There was a high rate of mental health problems in COVID-19 patients. Detecting and managing mental health problems should be considered standard care for COVID-19 patients.