Most of the bacterial pathogens are resistant to existing synthetic antibacterial agents demanding an increasing effort to seek effective phytochemicals as antibacterial agents against such pathogens. Nigella sativa L. (black cumin) seeds play an important role in folk medicine and some of its major constituents are reported to be pharmacologically active. In this present work, black cumin seed extracts were obtained using supercritical carbon dioxide (SCCO₂) and conventional soxtec extraction using various organic solvents. The antibacterial activities of the extracts were investigated by the agar dilution method against Gram-positive bacteria (Bacillus cereus F 4810 and Staphylococcus aureus FRI 722) and Gram-negative bacteria (Escherichia coli MTCC 108 and Yersinia enterocolitica MTCC 859). SCCO₂-1 (120 bar/40ºC) extract showed effective growth inhibition than conventional solvent extracts against all the tested bacteria. Further the antibacterial principle present in the extract was isolated and characterized found to be thymoquinone.