Mental arithmetic (MA) tasks have been reported to induce an increase in blood pressure and heart rate by enhancing sympathetic activity. However, there are individual differences in the change of autonomic nervous activity during MA task. In the present study, we quantitatively analyzed EEG changes and autonomic nervous activity using heart rate variability (HRV) during MA task in 38 healthy young volunteers. They were classified into two groups, stress responders and non-responders, according to whether both LF/HF and blood pressure increased above the baseline or not in response to MA. Then autonomic and EEG changes were compared between the two groups. The MA task induced an increase in slow beta power in the stress responders, whereas it induced a decrease in slow beta power in the stress non responders. Further evaluation showed a significant positive correlation between the percent change from the baseline in slow alpha power and that in LF/HF. These results suggest that there are correlations between the autonomic response in an individual and EEG power changes during MA tasks.