A series of 6,7-dihydro-[1,2,4]triazolo[5,1-b]quinazolin-8(5H)-ones, 4a–o were synthesized via a one-pot, multicomponent reaction in the presence of water as a solvent under microwave irradiation using ceric ammonium nitrate as an oxidizing agent. This techno-chemical method provides a rapid construction of higher molecules in short duration with high yield. The adopted method was carried out in the presence of water without catalyst and yielded the compounds without any side products, and thus further purification of compounds by column chromatography was not required. All the synthesized compounds, 4a–o were screened for their 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity. All the compounds, 4a–o possessed moderate antioxidant activity when compared to their standard antioxidant (ascorbic acid).