Introduction: Cardiac autonomic modulation can be altered by carbohydrate ingestion. On the other hand, some of the protective effects of physical activity may be due to its impact on the autonomic nervous system. Purpose This cross-sectional study was conducted to evaluate whether physical activity level influences heart rate variability (HRV) under fasting and mainly, after dextrose ingestion. Methods Healthy adults aged 18–40 years (n = 92; 54.35 % women) were separated into nonactive (n = 47) and active groups (n = 45), based on the physical activity level determined by International Physical Activity Questionnaire (IPAQ) and then compared. Results There were no significant differences (P > 0.05) for age, body mass, BMI, abdominal circumference, blood pressure, fasting glucose and blood glucose at 60 min after dextrose ingestion between groups. Body fat (%) was lower in the active group (P = 0.02). The time-domain indices (RMSSD, SDNN and pNN50) were higher in the physically active group compared to the nonactive group (main effect of group, P < 0.01). The SDNN index was higher at 60 min after dextrose ingestion compared to fasting (main effect of time, P ≤ 0.01). However, no HRV indices showed significantly interaction effect (group x time; P > 0.05). Conclusion The magnitude of HRV responses to glucose was not influenced by physical activity status. Young adults who met at least the minimum physical activity recommendations showed a higher cardiac autonomic modulation, regardless of dextrose ingestion.