A series of 4-substituted 3,4-dihydropyrimidine-2-ones (DHPM) was synthesized, characterized by IR, 1H NMR, 13C NMR and HRMS spectra. The compounds were evaluated in vitro for their antiviral activity against a broad range of DNA and RNA viruses, along with assessment for potential cytotoxicity in diverse mammalian cell lines. Compound 4m, which possesses a long lipophilic side chain, was found to be a potent and selective inhibitor of Punta Toro virus, a member of the Bunyaviridae. For Rift Valley fever virus, which is another Bunyavirus, the activity of 4m was negligible. DHPMs with a C-4 aryl moiety bearing halogen substitution (4b, 4c and 4d) were found to be cytotoxic in MT4 cells.