Purpose: Available research on mobile learning all stand on the viewpoint of teachers. However, as mobile learning is learner-centric, learners' roles must be understood clearly from the learners' viewpoint, particularly considering its self-directed learning feature. It is well-known learners for self-directed learning must bear some teachers' core responsibilities. The knowledge gap on this important issue inspires the present work which tries to answer two questions: which "teacher roles" can learners play and how will learners play their "teacher roles" in a mobile learning context. This study aims to discuss the aforementioned objectives. Design/methodology/approach: A novel research approach integrating an action research model and a teaching presence scale analysis is proposed to answer the questions. The mobile learning courses conducted by the present authors for engineering undergraduate students, during the COVID-19 pandemic, provided the experimental data for this study. Findings: The experimental results reveal that the learners could play a number of "teacher roles" actively for mobile learning. Some of this research studies are consistent with available studies but a discrepancy is also observed. Discussion is conducted for such discrepancy. Originality/value: The findings will contribute to improve the pedagogy of mobile learning theoretically and practically.