This study aimed to examine how moderate-to-vigorous physical activity (MVPA) during concussion recovery influences self-reported anxiety symptoms at follow-up assessment. We hypothesized that more MVPA after concussion would be associated with lower anxiety rating at follow-up. We performed a prospective study of participants aged 13-18 yr initially assessed within 14 d of diagnosed concussion. Participants rated concussion symptoms using the Post-Concussion Symptom Inventory and were provided a wrist-worn actigraphy device to track activity for 1 wk after assessment. At follow-up assessment, participants rated anxiety symptoms using the four-question Patient-Reported Outcomes Measurement Information System (PROMIS) anxiety subscale. Each question ranged from 1 (never) to 5 (almost always), with an overall score range of 4-20. For univariable analysis, we calculated correlation coefficients between MVPA and PROMIS anxiety subscale scores. We then created a multiple linear regression model with follow-up PROMIS anxiety subscale score as the outcome and MVPA, sex, initial symptom severity, and preconcussion anxiety as predictors. We enrolled and initially tested 55 participants, and 48 were included in the final analysis (age, 14.6±2.7 yr; 56% female; initial assessment, 7.3± 3.1 d; follow-up assessment, 42.0±29.7 d). We observed an inverse and low correlation between MVPA and follow-up PROMIS anxiety subscale T-scores ( r = -0.30, P = 0.04). Multivariable regression results indicated that MVPA ( β = -5.30; 95% confidence interval (CI), -10.58 to -0.01), initial Post-Concussion Symptom Inventory score ( β = 0.11; 95% CI, 0.03 to 0.19), and preconcussion anxiety ( β = 5.56; 95% CI, 0.12 to 11.0), but not sex ( β = -2.60; 95% CI, -7.14, to 1.94), were associated with follow-up PROMIS anxiety subscale T-scores. After adjusting for covariates, more MVPA early after concussion predicted lower PROMIS anxiety subscale scores at follow-up. Although initial concussion symptom severity and preconcussion anxiety were also associated with follow-up PROMIS anxiety subscale score, MVPA represents a modifiable factor that may contribute to lower anxiety symptoms.