Health crises across the globe bring dramatic changes to the lives of individuals and organizations. These crises have some psychological effects on society. The COVID-19 pandemic also caused some serious problems for individual and organizational life. Globally, the COVID-19 situation precipitated various economic and psychological issues that are far-reaching and exceptional. Health crises are increasing following the occurrence of COVID-19 due to its psychological effects on individuals worldwide. The current study highlighted the impact of COVID-19 fear on mental well-being (MWB). Most studies have examined the MWB of nursing staff and related their MWB to psychological factors. Few studies have considered the health crisis factors that are important in terms of bringing about variation in the MWB of nursing staff. Nursing staff MWB is impacted by various health crises (including COVID-19) at the global level and it has been ignored by researchers. In this study, a list of 1940 healthcare units with 6758 nursing staff was obtained. A total of 822 nurses were selected with the help of random sampling. The collected data were analyzed using correlation analysis, SPSS (statistical package for social sciences) version 23, and SEM. Thus, in this study we examined the effect of a health crisis (i.e., COVID-19) fear on the MWB of nurses. Moreover, we also examined the extent to which perceived stress (PS) influences the link between COVID-19 fear and MWB. The study's findings confirmed that COVID-19 fear shown negative effect on MWB, while PS mediated the link between COVID-19 fear and MWB.