Microwave processing and cooking of foods is a recent development that is gaining momentum in household as well as large-scale food applications. Barley contains phenol compounds which possess antioxidant activity. In this study the microwave oven roasting condition was optimized to obtain grains with high antioxidant activity measured as the ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical. Antioxidant activity of grains roasted under optimum conditions was assessed based on DPPH radical scavenging activity, reducing power and inhibition of oxidation in linoleic acid system. The optimum condition for obtaining roasted barley with high antioxidant activity (90.5% DPPH inhibition) was found to be at 600 W microwave power, 8.5 min roasting time, and 61.5 g or 2 layers of grains. The roasting condition influenced antioxidant activity both individually and interactively. Statistical analysis showed that the model was significant (P < 0.0001). The acetone extract had significantly high inhibition of lipid peroxidation and DPPH radical scavenging activity compared to the aqueous extract and alpha-tocopherol. The reducing power of acetone extracts was not significantly different from alpha-tocopherol. The acetone extract had twice the amount of phenol content compared to the aqueous extract indicating its high extraction efficiency. GC-MS analysis revealed the presence of phenol acids, amino phenols, and quinones. The aqueous extract did not contain 3,4-dihydroxybenzaldehyde and 4-hydroxycinnamic acid which are phenol compounds reported to contribute to antioxidant activity in barley grain.