This study aimed to investigate the relationship between athletes’ mindfulness and discrepancy in their self-evaluated and teammate-evaluated performance decrement. The participants in this study were 120 university athletes who took part in a longitudinal survey at three time points. The participants first answered a survey to rate their mindfulness and own performance decrement. Then, they partnered with a teammate and evaluated each other's performance decrement. The participants were classified into a high mindfulness group and low mindfulness group based on their mindfulness score. A three-factor analysis of covariance (group × time × evaluator) was conducted. The two-way interaction between group and evaluator was significant. A simple main effect analysis showed that the low mindfulness group scored higher on performance decrement than the high mindfulness group in self-evaluation, whereas no difference was observed between the groups in terms of teammate evaluation. Therefore, it was inferred that athletes with low mindfulness are more likely to evaluate their own performance negatively compared to athletes with high mindfulness, even when their teammates do not.