A number of studies have shown that prosocial behavior is associated with enhanced well-being, but most prior experimental studies have involved actual or potential face-to-face contact with the beneficiary. To establish that it is prosocial behavior itself, and not only an increased sense of social relatedness to the recipient that improves well-being, participants (n = 76) were invited to play a simple computer game, where half were made aware of a chance to have an anonymous prosocial impact through gameplay. As compared to the control condition, this group experienced more positive affect, meaningfulness and marginally more vitality. Going beyond self-reported outcomes, they also demonstrated better post-game performance on a subsequent Stroop task, providing behavioral evidence for the positive effects of prosocial behavior. Also supported was the hypothesis that these positive effects of prosocial behavior on well-being were mediated by subjectively assessed autonomy and competence need satisfactions.