In recent years, online courses have become a prevalent mode of study in English as a Foreign Language (EFL) university education. Student engagement is widely recognized as a key factor that influences students' quality of learning and academic achievement. This study explored the predictive impacts of self-efficacy, teacher support, and positive academic emotions on student engagement in online courses. The participants were 201 Saudi university students studying English as a foreign language. The data were collected and analyzed quantitatively using structural equation modeling techniques. The findings showed that self-efficacy and positive academic emotions significantly predicted online student engagement. However, teacher support did not have a significant effect on online student engagement. Overall, the findings obtained hold significant merits for further research development and educational practices.