The COVID-19 pandemic and the associated restrictions caused great psychological suffering to the general population and psychiatric patients. We aimed to explore the course of depression and anxiety symptoms in obsessive compulsive disorder (OCD) patients, adjustment disorder (AD) patients, and participants without psychiatric disorders (control group, CG) across the different phases of the pandemic: the first lockdown, a temporary interruption of restrictions, and the second lockdown. Out of the 158 patients screened, we enrolled 46 OCD and 19 AD patients as well as 29 CG participants. The Beck Depression Inventory-II and the State-Trait Anxiety Inventory-Y were administered to all participants at each time point. The results showed different symptom severities among the groups throughout the whole study, with OCD patients always scoring higher than AD patients and the CG, and the AD patients always scoring higher than the CG. The symptom course within each group was different. OCD patients’ symptoms sharply worsened during the first lockdown and then remained stable irrespective of the subsequent pandemic phases. In the AD and CG groups, symptoms waxed and waned following the fluctuations of the restriction provisions, with a complete return to the baseline when the restrictions were stopped only in the CG. These findings suggest that the influence of the pandemic and of the associated restrictions on depression and anxiety manifestations may vary depending on the particular pre-existing mental health status.