In Japan, a rapidly aging society with a declining birthrate has led to an increased caregiving burden on younger generations. Dementia, often preceded by mild cognitive impairment (MCI), requires early intervention to prevent progression, which necessitates monitoring MCI and related brain changes. However, traditional methods, such as computed tomography (CT), magnetic resonance imaging (MRI), and medical electroencephalography (EEG), are costly and physically demanding for elderly individuals. This study examines the feasibility of using a simple headband-type EEG device during cognitive function tests to identify early dementia markers. This study investigates the effects of cognitive function testing on EEG activity by comparing EEG data obtained from two groups: younger healthy adults (19 subjects; mean age ± standard deviation (SD): 21.07 ± 1.38 years) and older healthy adults (15 subjects; mean age ± SD: 77.07 ± 5.37 years). The Mann-Whitney U test was used to analyze their EEG power spectral density (PSD). Significant differences were observed in the β and γ bands during the Clock Drawing Test (CDT) and in the δ band of the right hemisphere during the Spiral Drawing Test (SDT). However, no significant differences were observed on the Revised Hasegawa’s Dementia Scale (HDS-R). These findings suggest that δ band abnormalities during the Spiral Drawing Test and β and γ band changes during CDT could serve as potential biomarkers for early MCI symptoms. Hence, this approach offers a less invasive and cost-effective alternative for early dementia detection, potentially easing the burden on healthcare systems while supporting timely interventions.