While conspiracy theories have received extensive attention in the realm of misinformation, there has been limited research exploring the impact of conspiracy mentality on individuals' preventive behaviors during acute public health crises. This study investigates how conspiracy mentality may affect compliance with preventive health measures necessary to fight the COVID-19 pandemic, and the underlying emotional and cognitive mediators. Data was collected through a survey among 1878 Chinese respondents at the conclusion of the pandemic. The results indicate that individuals with higher levels of conspiracy mentality are significantly less engaged in preventive behaviors. Furthermore, this correlation is mediated by a sequence of mediating factors, starting from anger leading to institutional distrust and fear leading to perceived risk. Conspiracists' response mode can be described as a state of "attentive immobility," in which the impact of heightened institutional distrust outweighs their perceptions of risk, ultimately reducing engagement in preventive behaviors during crises. These findings underscore the importance of debunking initiatives that aim to address and mitigate the negative consequences of conspiracy mentality by targeting the mediating psychological processes during future pandemic threats.