Students’ non-posting behaviour in online discussions is often neglected in educational research. However, it can be a potential indicator of student learning. This study examined the relationships between motivation, peer feedback and students’ posting and non-posting behaviours in online discussions in a distance learning class. Fifty-seven college students participated in collaborative learning activities through online discussions. Their posting and non-posting behavioural data were tracked automatically in the discussion system. Results show that students spent a significant amount of time participating in non-posting activities. Motivation and peer feedback predicted both posting and non-posting behaviours in online discussions.