The use of microorganisms in the synthesis of nanoparticles emerges as an eco-friendly and exciting approach. In this study, we report on the use of Bacillus cereus for the extracellular synthesis of silver nanoparticles (Ag NPs) from silver nitrate solution. Ag NPs were characterized by UV-vis spectroscopy, fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). UV-vis spectroscopy of Ag NPs exhibited peak at 440 nm which corresponds to the surface plasmon resonance of Ag NPs. FTIR spectroscopy confirmed the presence of protein as the stabilizing agent surrounding the Ag NPs. AFM of Ag NPs showed irregular shape with 62.8 nm in size. Antimicrobial activity of the silver bio-nanoparticles was performed by well diffusion method against Staphylococcus aureus, Salmonella typhi, Klebsiella pneumoniae and Escherichia coli. The highest antimicrobial activities recorded were against Staphylococcus aureus followed by Klebsiella pneumoniae and Salmonella typhi, where as Escherichia coli showed the lesser activity.