Yoga is a promising strategy for promoting positive body image. However, certain social-environmental variables might undermine yoga’s benefits. Previous research indicates that mirrors alter women’s psychological responses to exercise, but the effects of practicing yoga with mirrors are unknown. The present study examined the effect of mirrors on women’s state body image, affect, and self-efficacy in a yoga class. A secondary aim was to examine the effect of mirrors on social comparison and mindfulness. Potential moderators were also examined. Ninety-seven college-aged females were randomly assigned to complete a 60-minute beginner level yoga class in either a mirrored or non-mirrored setting. Surveys were completed prior to and immediately after class. As hypothesized, the non-mirrored condition had significantly lower state social physique anxiety (SPA) after yoga than the mirrored condition. The mirrored condition reported significantly higher appearance-based social comparison than the non-mirrored condition, and social comparison mediated the relationship between mirrors and state SPA. There were no significant moderator effects. Mirrors appeared to lead to higher levels of state SPA in the mirrored vs. non-mirrored condition by fostering appearance comparisons with other participants and the yoga instructor. To encourage internal body awareness and minimize appearance comparisons in yoga classes, instructors in mirrored studios may want to consider structuring classes so students face away from mirrors, and reminding students to focus on how poses feel rather than how they look. Additional research examining the longer-term psychological effects of regularly practicing yoga with mirrors is merited.