Background: Self-efficacy and the use of learning activities in online learning platforms have been extensively researched recently and are considered factors of online learning success. However, little research empirically seeks the correlation between those variables, including in English as a foreign language (EFL) online classes. Purpose: To investigate whether there is a significant correlation between the use of online learning platforms and EFL students' self-efficacy in online learning in English classes. Method: This quantitative research used two questionnaires, i.e., the Online Learning Platform Questionnaire (OLPQ) and the Self-Efficacy Questionnaire for Online Learning (SeQoL). The use of online learning platforms measured in this study includes independent learning, virtual meetings, forum discussion, collaborative learning, and assessment; meanwhile, self-efficacy includes course completion, social interaction, academic interaction, interaction with lecturers, and the use of LMS. The sample of this research was 133 EFL students from three universities in Indonesia. The data was analyzed using Spearman's correlation at the significance level of 0.05. Results: The results show that independent learning, collaborative learning, and forum discussion correlate with most constructs of self-efficacy. Meanwhile, the results indicate no correlation between two constructs of online learning platforms, namely virtual meetings and assessments, and three constructs of self-efficacy, i.e., students’ social interaction, academic interaction, and students’ interaction with lecturers. Conclusion: This research shows that more frequent use of online learning platforms, especially those covering independent learning, collaborative learning, and forum discussion, results in higher confidence among EFL students to succeed in online learning. Suggestion: Therefore, this research suggests that lecturers consider using significant features of online learning platforms to enhance students’ self-efficacy in online EFL classes.