Innovative technologies, such as the Audience Response System (ARS) provide an opportunity to steer students into active engagement and meaningful discussions. Many previous studies on the use of ARS, mainly in large traditional classes, have accentuated the positive impact in terms of increased students’ learning and engagement through the incorporation of ARS into classroom practices. However, in synchronous online courses, wherein the lack of visual contact tends to stifle active engagement, the impact of using ARS is certainly worthy of investigation. Thus, in this mixed method study, online English as a Foreign Language (EFL) students’ perceptions concerning the use of mobile-based ARS (M-ARS) and its impact on enhancing their engagement, interactivity, and learning attainment were examined via a questionnaire whereas challenges pertaining to the use of M-ARS were solicited via semi-structured interviews. The results revealed that the implementation of M-ARS in online teaching correlate significantly with EFL students’ engagement and learning experience whereas qualitative analysis revealed some important points with regard to integrating M-ARS into online classrooms. Directions and suggestions for future research are offered.