Winning against an opponent in a competitive video game can be expected to be more rewarding than losing, especially when the opponent is a fellow human player rather than a computer. We show that winning versus losing in a first-person video game activates the brain's reward circuit and the ventromedial prefrontal cortex (vmPFC) differently depending on the type of the opponent. Participants played a competitive tank shooter game against alleged human and computer opponents while their brain activity was measured with functional magnetic resonance imaging. Brain responses to wins and losses were contrasted by fitting an event-related model to the hemodynamic data. Stronger activation to winning was observed in ventral and dorsal striatum as well as in vmPFC. Activation in ventral striatum was associated with participants' self-ratings of pleasure. During winning, ventral striatum showed stronger functional coupling with right insula, and weaker coupling with dorsal striatum, sensorimotor pre- and postcentral gyri, and visual association cortices. The vmPFC and dorsal striatum responses were stronger to winning when the subject was playing against a human rather than a computer. These results highlight the importance of social context in the neural encoding of reward value.