The mechanisms that the brain uses to discriminate between odors have long been a research focus. Previous studies suggest that odor categorization may involve multiple neurological processes within the brain (i.e. temporal and spatial neuronal activation and systemic phase synchronization); there is limited evidence regarding temporally mediated mechanisms in humans, especially in early response periods (<200 ms). Here, we focus on how the brain discriminates odors during early olfactory responses. Combined with a multi-variable electroencephalography (EEG) analysis, we show that similarly perceived odors induce similar EEG oscillation activity including theta, beta, and gamma waves during early olfactory responses. Furthermore, sLORETA analysis showed that EEG oscillation activity source localized from olfactory related brain area such as OFC. These are the first evidences that systemic brain activity may be related to odor processing, specifically odor quality similarity, during early olfactory responses.