ADHD, the common neurodevelopmental disorder affecting children, is reported with a prevalence of 2.1% to 5.7% among preschool-aged children. To assist the early diagnosis, clinicians usually refer to the instrument, Conner's kiddie continuous performance test; however, the test lacks the event markers of the task stimuli, which are essential information for task-related EEG study. We conducted artifact removal, extracted, separated, and allocated the recorded raw EEG signals into resting, fast-rate task, and slow-rate task segments to investigate the dynamic changes between groups with ADHD and controls. The slow-rate task related band power and alpha power alterations within conditions were distinct between groups. The methodology in our study is practical for EEG data analysis regarding different task conditions.