Avenanthramides, the phenolic antioxidants exclusively found in oats (Avena sativa L.), have long been recognized for their immense health benefits owing to their antioxidant potential. Herein, hydroperoxyl radical ( • OOH) scavenging activity of oat avenanthramides is investigated in detail, using density functional theory for the first time. Three probable mechanisms: (a) hydrogen atom transfer (HAT), (b) single electron transfer followed by proton transfer, and (c) sequential proton loss electron transfer (SPLET), are considered towards evaluating the antioxidant potential of avenanthramides (A-C) in the gas phase as well as in both polar and non-polar media. Based on the computed data, HAT is found to be the thermodynamically preferred mechanism for antioxidant activity in the gas phase. In the polar medium, SPLET represents the most probable reaction pathway. Our thermodynamic and kinetic data computed at the B3LYP level predict avenanthramide C, characterized by an ortho-dihydroxy functionality on the aromatic ring, as the most potent radical scavenger among the three variants, in agreement with the available experimental reports.