Background: Cumin (Cuminum cyminum L. [family Apiaceae]) seed essential oil is reported to have antiseptic activity. Until now the antiviral properties of cumin seed extracts on viruses such as herpes simplex virus-1 (HSV-1) have not been studied. The objective of this study was to investigate the in vitro effects of aqueous, methanolic and hydroalcoholic extracts of cumin seed on HSV-1 growth in Vero cell line. Methods: Antiviral activity of various concentrations aqueous, hydroalcoholic and methanolic extracts of cumin seed in Vero cells were studied using plaque reduction assays. The 50% cytotoxic concentration (CC50), 50% inhibitory concentration (IC50), and therapeutic index of the effective extracts were calculated. Results: Methanolic extract of cumin seed showed a significant antiviral activity on HSV-1 in Vero cell line. Its CC50 for Vero cells, IC50 and the therapeutic index for HSV-1 were 0.45, 0.18 mg/mL and 2.5, respectively. Aqueous and hydroalcoholic extracts of cumin seeds showed no inhibitory effect on HSV-1. Conclusion: The methanolic extract of cumin seed produces anti-HSV-1 effect. Probable interference of phenolic compounds with fusion of Vero cell membrane and HSV-1 envelope might be the mechanism of such inhibitory effect. Further studies are required to ascertain its in vivo antiviral properties and potential toxicity.