Frontotemporal dementia (FTD) is the second most common form of presenile dementia; however, its diagnosis has been poorly investigated. Previous attempts to diagnose FTD using quantitative electroencephalography (qEEG) have yielded inconsistent results in both spectral and functional connectivity analyses. This study aimed to introduce an accurate qEEG marker that could be used to diagnose FTD and other neurological abnormalities. We used open-access electroencephalography data from OpenNeuro to investigate the power ratio between the frontal and temporal lobes in the resting state of 23 patients with FTD and 29 healthy controls. Spectral data were extracted using a Fast Fourier Transform in the delta (1–4 Hz), theta (4–8 Hz), alpha (8–13 Hz), beta (13–32 Hz), and gamma (32–45 Hz) bands. We found that the spectral power ratio between the frontal and temporal lobes is a promising qEEG marker of FTD. Frontal/temporal (F/T) theta/alpha, alpha/theta, al-pha/gamma, and gamma/alpha showed a consistently high discrimination score for the diagnosis of FTD for different parameters and referencing methods. The study findings can serve as reference for future research focused on diagnosing FTD and other neurological anomalies.