Nepeta nuda subsp. nuda L. is a valuable medicinal plant well-known for its various therapeutic properties. This study assessed the antiviral activity of four extracts derived by methanol and chloroform extractions from in vivo grown and in vitro propagated plants. The cytotoxicity was tested on Madin–Darby bovine kidney (MDBK) cell line. Maximal tolerated concentration (MTC) and cytotoxic concentration (CC50) of both extracts were determined. Antiviral activity on viral replication was evaluated against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) in MDBK cell line. The 50% inhibitory concentrations (IC50) and selective index (SI) of the extracts against both viruses were calculated. The methanol extract, derived from the native plant exhibited the greatest antiviral activity. The IC50 for both viruses was similar – 320 μg/mL against HSV-1 and 510 μg/mL against HSV-2. The SI were 4.94 and 3.1, respectively. Applied in MTC, the extract inhibited viral replication by more than 95% in both HSV-1 and HSV-2. The virucidal effect was determined by the reduction of the infectious virus titer. All four extracts of N. nuda inactivated the extracellular form of HSV-2. The major virucidal activity was demonstrated by the chloroform extract from the native plant – more than 99% viral inactivation. The extracts weakly affected the viral entry into the host cell. The highest inactivation was shown by the chloroform extract form the native plant – more than 90%.