Mental health disorders are the leading cause of health-related problems globally. It is projected that mental health disorders will be the leading cause of morbidity among adults as the incidence rates of anxiety and depression grows globally. Recently, extended reality (XR), a general term covering virtual reality (VR), augmented reality (AR) and mixed reality (MR), is paving a new way to deliver mental health care. In this paper, we conduct a scoping review on the development and application of XR in the area of mental disorders. We performed a scoping database search to identify the relevant studies indexed in Google Scholar, PubMed, and the ACM Digital Library. A search period between August 2016 and December 2023 was defined to select articles related to the usage of VR, AR, and MR in a mental health context. We identified a total of 85 studies from 27 countries across the globe. By performing data analysis, we found that most of the studies focused on developed countries such as the US (16.47%) and Germany (12.94%). None of the studies were for African countries. The majority of the articles reported that XR techniques led to a significant reduction in symptoms of anxiety or depression. More studies were published in the year 2021, i.e., 31.76% (n = 31). This could indicate that mental disorder intervention received a higher attention when COVID-19 emerged. Most studies (n = 65) focused on a population between 18 and 65 years old, only a few studies focused on teenagers (n = 2). Also, more studies were done experimentally (n = 67, 78.82%) rather than by analytical and modeling approaches (n = 8, 9.41%). This shows that there is a rapid development of XR technology for mental health care. Furthermore, these studies showed that XR technology can effectively be used for evaluating mental disorders in similar or better way as the conventional approaches.