Developing low cost and environmentally friendly methods for metallic nanoparticles is an increasing need. Using plants towards synthesis of nanoparticles are beneficial with the presence of bio-molecules in plants, which can act as capping/stabilizing and reducing agents. In the present attempt, we describe rapid biosynthesis of silver nanoparticles by Satureja intermedia C. A. Mey (Lamiaceae) aqueous extract. Synthesized nanoparticles were characterized by UV-Visible spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and the chemical groups in plant extract were detected by Fourier Transform Infra-Red (FT-IR) spectroscopy. The XRD study showed crystalline nature and face cubic center shape for nanoparticles. TEM study showed that the mean diameter and standard deviation for the silver nanoparticles were 29.29 ± 28.18 nm. Total phenolic and flavonoid contents and radical scavenging activity of the aqueous extract and SNPs/extract mixture, were also evaluated in this study. It can be concluded that the aerial parts of S. intermedia is a good source of phenolic compounds, a potent antioxidant and a valuable choice for bio-reduction and biosynthesis of silver nanoparticles.