Background: Little is known about psychiatric patients’ experiences during the COVID-19 pandemic. The purpose of this study was to investigate associations of coping strategies, social support and loneliness with mental health symptoms among these patients. Methods: We recruited 164 patients from Community Mental Health Centers in June–July 2020. Participants responded to an online questionnaire on corona-related questions, Brief Coping Orientation to Problems Experience, Crisis Support Scale, a 3-item Loneliness Scale, and Hopkins Symptom Checklist-25. We used linear regression models to investigate associations between these and symptoms of depression and anxiety. Results: Almost 51% were aged 31–50 years and 77% were females. Forty-six (28%) participants reported worsened overall mental health due to the pandemic. The reported rates of clinical depression and anxiety were 84% and 76%, respectively. Maladaptive coping was independently associated with both depression and anxiety symptoms. Loneliness was independently associated with depression symptoms. Conclusions: Patients in Community Mental Health Centers in Norway reported high rates of depression and anxiety symptoms. Many of them reported worsening of their mental health due to the pandemic, even at a time when COVID-19 infections and restrictive measures were relatively low. Maladaptive coping strategies and loneliness may be possible explanations for more distress.