Popcorn, one of the most popular snack foods in the world, is known for being a high fiber, healthy food. Our research has found that commercial popcorn also contains significant amounts of the class of antioxidants known as phenolic acids. The total antioxidant capacity of raw and popped popcorn extract has been quantified using the Folin–Ciocalteu and FRAP assays. The polyphenols were found exclusively in the pericarp of the kernel completely bound to the oligosaccharide fiber matrix. An in vitro digestion study was also performed to predict the phenolic acids’ bioavailability. On average, nine commercial popcorn samples contain 5.93 ± 0.92 mg/g of total polyphenols after alkaline hydrolysis and 2.66 ± 0.15 mg/g after in vitro digestion as measured by the Folin–Ciocalteu assay. Furthermore, the popping process was found not to significantly decrease the antioxidant capacity. These results indicate that a considerable amount of the bound polyphenols are bioaccessible. Due to the high levels of bioaccessible polyphenols, popcorn may be a significant source of dietary polyphenol antioxidants.