This exploratory study examines emotional affordance of a massive open online course (MOOC). Postings in a discussion forum of a MOOC in computer science are analysed following a research design informed by virtual ethnography. Emotional affordance is investigated, focusing on non-achievement emotions which are not directly linked to achievement activities or outcomes. The study identifies two non-achievement emotions in the MOOC. First, altruistic emotion evolves with the collaborative learning community and possibly compensates for teachers' minimal emotional intervention in a large, diverse class. Second, intergenerational emotional resonance is observed and this bears a key implication on managing age diversity for the future MOOCs.