Aims: This study aimed to investigate the effect of a blended educational intervention based on the health belief model (HBM) about COVID-19 on teachers' preventive behavior. Materials & Methods: A randomized controlled trial was conducted on female teachers in four districts affiliated with Education Organization Karaj Iran. Then, one of these two districts was assigned to the intervention group (n=70) and the other to the control group (n=70) by the lottery method. The educational intervention was conducted via three online platforms. Our intervention was named BEHTA. It included a specifically designed website, holding virtual and group discussion classes, and using a popular social network messenger. Findings: The results showed that there was no significant difference between the intervention and control groups before training (p>0.05) but immediately and 12 weeks after training, the two groups had a statistically significant difference in all constructs (p<0.05). In the control group, the mean score of knowledge, perceived susceptibility, perceived severity, perceived benefits, perceived barriers, cues to action, and self-efficacy did not differ significantly (p>0.05), but the mean score of behavior decreased (p=0.027). Conclusion: The educational intervention improves all constructs regarding COVID-19 in the intervention group.