Coronavirus disease-19 (COVID-19) caused by a new emerging virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), led to a major public health crisis worldwide, including Korea in 2020. Infected people may experience a wide spectrum of COVID-19-related physical and mental symptoms and psychosocial difficulties, including abrupt isolation, being blamed by others, death of a loved one by COVID-19, and financial loss. Although the data is limited so far, a recently growing number of studies suggest that the mental health of COVID-19 patients could be negatively affected in terms of anxiety, depression, post-traumatic stress symptoms, and cognitive impairment during the treatment and even after the cure. The severity of the disease, previous psychiatric history, and perceived stigma might be risk factors, while social support might be a protective factor. Quarantined people without COVID-19 also can have mental health issues from loneliness to suicidality according to their condition and experiences during isolation. With increasing interest in COVID-19-related mental health issues, psychosocial support is an essential part of care for the infected and the quarantined. Furthermore, respect for human rights, including efforts to respect individual vulnerability and reduce stigma and discrimination, and building social trust could be potent preventive measures for mental health in the pandemic crisis. Well-designed studies will be needed to identify the short- and long-term effects of COVID-19 on mental health in those groups and develop effective strategies.