Objective: The present study aimed to review the presentations of attention-deficit/hyperactivity disorder (ADHD) based on brain frequency bands through quantitative electroencephalogray (QEEG). Method: This study used the review method to determine the differences between modern theories in terms of ADHD diagnosis and classification. Results: Theoretical review revealed that the number of studies on brain activity in those with ADHD has increased in the past decade. Although the Diagnostics and Statistical Manual of Mental Disorders (DSM-5) defines three ADHD clinical phenotypes (attention difficulties, hyperactivity /impulsivity, and the combined subtype), a QEEG spectrum classification of ADHD population has recently been developed, defining four main subtypes: Subtype I (abnormal increase of delta-theta frequency range centrally or centrally-frontally), Subtype II (abnormal increase of frontal midline theta rhythm), Subtype III (abnormal increase of beta activity frontally), and Subtype IV (excessive alpha activities at posterior, central, or frontal leads). Conclusion: Although this classification has been implied in various studies, comprehensive investigation is required for it to be established in diagnosis. The present review illuminated the theoretical and experimental basis of the QEEG spectrum classification of ADHD.