Quantitative EEG evaluation in Parkinson disease (PD) reveals diffuse slowing. This is the first quantitative EEG evaluation of the differences between PD with and without executive dysfunction (ExD). The subjects were 32 PD patients without remarkable dementia. The lack of ischemic lesions was confirmed by magnetic resonance imaging. ExD was defined as <70 points on the age-controlled standardized score of the Behavioral Assessment of the Dysexecutive Syndrome. Absolute power was measured for four frequency bands from delta to beta. Electrodes were placed at frontal pole, frontal, central, parietal, occipital, and temporal locations. Spectral ratio was calculated as the sum of power values for alpha and beta waves divided by the sum of values for the slow waves. In multiple logistic regression analysis of each electrode location, the dependent variable was ExD or not, and the independent variables were spectral ratio, age, and Unified Parkinson Disease Rating Scale. The only significant predictor of ExD was spectral ratio at the frontal pole (P = 0.031) and frontal (P = 0.048) locations. PD with ExD exhibited an increase in slow wave activity and a decrease in alpha and fast wave activities in these locations. These findings indicated that the ExD in PD was caused by frontal dysfunction.