The influx of nanoparticles into the living systems especially for medical purposes has opened up a new challenge of synthesizing them in a benign fashion. Green synthesis of nanoparticles is looked upon as an alternative to the existing physical and chemical methods of syntheses as they are associated with undeniable disadvantages. This initiated the biogenic synthesis of nanoparticles by using various microorganisms and plants. In this study we report the use of endophytic bacterium Bacillus cereus isolated from the Adhatoda beddomei to synthesize the silver nanoparticles (AgNPs). The AgNPs were synthesized by reduction of silver nitrate (AgNO3) solution by the endophytic bacterium after incubation for 3 days at room temperature. The synthesis was initially observed by colour change from pale white to brown which was further confirmed by UV - Vis spectroscopy. The AgNPs were characterized using FTIR, SEM – EDAX and TEM. The synthesized nanoparticles were found to be spherical and uniformly distributed with the size in the range of 11-16 nm. The energy-dispersive spectroscopy of the nanoparticle dispersion confirmed the presence of elemental silver. The AgNPs were found to have reasonable antibacterial activity against a few pathogenic bacteria like Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. Determining the minimum inhibitory concentration leading to inhibition of bacterial growth is still under way.