This study reports on a mixed methods study which explored 32 Iranian pre-service teachers' perceptions of attending online asynchronous discussion forums during two seven-week online introductory courses in corpus linguistics. Data were collected through a questionnaire, discussion forum entries and online text-based semi-structured interviews. The quantitative and qualitative analysis of data revealed that the participants took part in the discussions mainly to express their attitudes, beliefs and evaluations; yet they were hesitant to express their emotions, answer their peers' questions, critique others' views, express acknowledgements and make references to other sources. The participants felt that online discussions should bring about meaningful, relevant and useful learning outcomes and help them understand the course topics rather than develop social relationships. The findings can help online instructors in postgrad education to manage effective online communication practices.