This study investigated players' emotional responses to performance feedback in an educational game under cooperative and competitive structures. A 2 × 2 repeated-measures experiment was conducted with the task structure (cooperative and competitive) and the task demand (low and high) as independent variables. Thirty-two students from a university campus participated in the experiment. We designed a memory game involving a humanoid robot as a co-player, manipulating cooperation and competition between the human player and the robot. Functional near-infrared spectroscopy (fNIRS) scanner was employed to monitor the participant's prefrontal cortex activity. The subjective experience was measured with questionnaires. fNIRS results showed that, compared to negative feedback, positive feedback led to increased activations in the orbitofrontal cortex and rostromedial cortex regardless of the task demand. Additionally, compared to competitive structures, cooperative structures caused increased activation in the left rostromedial region in low-demand tasks. Furthermore, participants reported a more positive self-evaluation in competitive than cooperative structures but more positive evaluation toward the robot in cooperative than competitive structures. •Positive feedback activates the orbitofrontal cortex in educational games.•Positive feedback activates the rostromedial prefrontal cortex in educational games.•Players report higher self-evaluation in competitive than cooperative games.•Players report higher robot-evaluation in cooperative than competitive games.•Players experience marginally higher pleasantness after competition than cooperation.