Background: Due to the global COVID-19 pandemic, online learning became the only way to learn during this unprecedented crisis. This study began with a simple but vital question: What factors influenced the success of online learning during the COVID-19 pandemic with a focus on online learning self-efficacy? Objectives: The purpose of this study was to examine the structural relationship among self-efficacy (SE) in time management, SE in technology use, SE in an online learning environment, and learning engagement. Methods: The participants of the study were 1205 undergraduates who were enrolled in a residential undergraduate program in South Korea in spring semester, 2020. The online survey was administered to collect data for this research and the survey results were analyzed using structural equation modeling. Results and Conclusions: SE in technology use had a significant but negative influence on learning engagement and had a positive impact on SE in an online learning environment. SE in time management had a significant positive impact on SE in an online learning environment and learning engagement. SE in an online learning environment also significantly influenced learning engagement. Implications: SE in technology use itself did not enhance learning engagement. In addition, indirect effects of SE in technology use and SE in time management on learning engagement through SE in an online learning environment were confirmed in this study. This indicates the influential role of SE in an online learning environment on learning engagement of online learners.