Background: This study aimed to investigate COVID-19 protective behaviors of Iranian healthcare workers (HCWs) using an extended parallel process model (EPPM). Methods: This cross-sectional study was conducted online on a convenience sample of 418 Iranian HCWs in 2020. Data were gathered using a standardized electronic questionnaire published on the Porsline website, designed based on the EPPM, to assess the relationships between different constructs of EPPM and COVID-19 protective behaviors. For data analysis, statistical tests, such as descriptive tests, independent t-test, ANOVA, Pearson's correlation test, and multiple regression analysis, were performed in SPSS version 18. Results: Most participants (40.4%) were in the age group of 30-40 years, and most were female (70.6%). Significant associations were found between COVID-19 protective behaviors and EPPM constructs of perceived self-efficacy (r = 0.373, P = 0.000), perceived response efficacy (r = 0.120, P = 0.014), and intention (r = 0.462, P = 0.000). Perceived self-efficacy (P = 0.000, beta = 0.398) and behavioral intention (P = 0.000; Beta = 0.283) were predictors of protective behaviors. Also, 34.4% of the HCWs were involved in the danger control process. Conclusions: Only one-third of the HCWs contributed to the process of COVID-19 danger control. The HCWs' motivation for protection against COVID-19 depended on their perception of self-efficacy and their perceived efficacy of COVID-19 preventive behaviors. The present results can be used to design and implement training programs to improve the protective behaviors of HCWs.