Abstract Previous studies showed that optimistic bias is an important concept to influence individuals' health‐related behaviors. The current web‐based experimental study proposes that perceived susceptibility, perceived severity, proximity and perceived control are factors that influence one's optimistic bias. Optimistic bias was reduced when participants perceived high susceptibility because their perceived control decreased. Further, moderated moderated‐mediation analysis revealed the moderating role of (1) perceived severity between perceived susceptibility and perceived control and (2) proximity between perceived control and optimistic bias. The analyses of interaction effects empirically demonstrated that the effect of perceived susceptibility and perceived control on optimistic bias are contingent upon perceived severity and proximity. Theoretical and practical implications were discussed.