The COVID-19 pandemic has brought about changes in mental health occupational therapy. Research into these changes and the associated risks of relapse is insufficient. To explore the changes that have taken place in forms of occupational intervention (face-to-face and online) during the pandemic, and to analyze their association with subsequent relapses, a multicenter retrospective cohort study was carried out of 270 patients with mental disorder diagnoses under follow-up in day hospitals during 2020. Our results show that the frequency of face-to-face occupational therapy interventions decreased during lockdown and subsequently recovered. Interventions via telehealth increased during lockdown and have since been continued to a greater extent than before lockdown. Patients who received occupational intervention via telehealth relapsed less in the following six months (10.7% vs. 26.3%; χ2 = 10.372; p = 0.001), especially those who received intervention via videoconferencing (4.2% vs. 22%; χ2 = 5.718; p = 0.017). In conclusion, lockdown subsequent to the COVID-19 outbreak led to a reduction in face-to-face occupational therapy interventions, putting people with prior mental disorders at risk, while the implementation of telehealth tools helped reduce relapses.