Understanding the cognitive function of human brain is an important step in providing scientific evidence which could help us improve the condition of memory disorders, slow down its progress or at least help the patients retain some important matters. In this study, we aimed to provide additional scientific evidence with more insight on how the brain functions at a good/bad cognitive state than the usual statistical analysis. We introduced the brain activation measurement using baseline-normalized ERSP to determine the activation of EEG data from stimuli. These active points over a period of time could reflect brain synchronization due to stimuli. We also demonstrated the use of proposed measure on attention working memory data. The results indicate the potential of using the proposed measurement in categorizing the brain cognitive state and identifying some important factors to provide additional evidence to the field in the future.