Remembering to perform a delayed intention is termed prospective memory (PM). Often delayed intentions are shared by more than one person; however, there is a dearth of studies examining PM in social settings. We aimed to investigate whether the potential consequences of one's behavior across diverse group settings influence PM performance in event- and time-based tasks. A total of 207 participants were randomly allocated to either an individual, collaborative, or collaborative plus penalty motivation condition and were tested in a 2- or 3-person setting. For the time-based PM task, participants responded less timely in the individual motivation condition, whereas there was no difference between the collaborative motivation conditions. No significant effects were found for motivation condition on the event-based task or for group size on PM performance. Analyses of ongoing task performance revealed that participants' attention allocation policies change depending on how individuals prioritize the ongoing and PM tasks.