The coronavirus (COVID-19) pandemic is currently a global health threat attributed to negatively affecting the mental health and well-being of people globally. The purpose of the present study is to examine the mediating role of optimism-pessimism and psychological inflexibility in the relationship of coronavirus stress with psychological problems among Turkish adults. The sample of the study included 451 adults (55% women). Participants mainly consisted of young adults with a mean age of 23.30 years, ranging from 18 to 65 years (SD= 6.97). A mediation model indicated that coronavirus stress had a significant predictive effect on optimism-pessimism, psychological inflexibility, and psychological problems. Further, optimism-pessimism and psychological inflexibility mediated the effect of coronavirus stress on psychological problems in adults. Lastly, optimism-pessimism predicted the psychological problems of adults through psychological inflexibility. These results elucidate our understanding of the role of mediators in coronavirus stress and psychological health problems. The findings are useful in terms of providing evidence for tailoring interventions and implementing preventative approaches to mitigate the psychopathological consequences of COVID-19. Based on the present findings, the potential utility of Acceptance and Commitment Therapy is discussed within the context of COVID-19.