This online survey study aimed to compare the cognitive, affective, and behavioral constructs of health beliefs related to coronavirus disease 2019 (COVID-19) between sexual minority and heterosexual individuals in Taiwan. In total, 533 sexual minority and 1421 heterosexual participants were recruited through a Facebook advertisement. The constructs pertaining to cognition (perceived relative susceptibility to COVID-19, perceived COVID-19 severity, having sufficient knowledge and information on COVID-19, and confidence in coping with COVID-19), affect (worry toward COVID-19), and behavior (adoption of health-protective behaviors) in relation to health beliefs about COVID-19 were compared between sexual minority and heterosexual participants. The results indicated that sexual minority participants had lower perceived susceptibility to COVID-19, greater self-confidence in coping with COVID-19, and lower worry about COVID-19 and were less likely to maintain good indoor ventilation and disinfect their household than heterosexual individuals. Sexual orientation is the modifying factor for the Health Belief Model in the COVID-19 pandemic and should be taken into consideration when medical professionals establish prevention programs for COVID-19.