Effects of plasmonic coupling on blue laser induced positive and negative photoconductivity of chemically vapor deposited mono-layer graphene transferred onto SiO2/Si with or without silver nanoparticles in ambient atmosphere are reported. Ggraphene on silver nanoparticles coated SiO 2/Si exhibits negative and rapidly decreasing photoconductivity upon light illumination. The photoconductivity recovers gradually and then become positive photoconductivity. In the subsequent on-off cycles of light illumination, the graphene exhibits positive photoconductivity. Graphene on SiO2/Si without silver nanoparticles also exhibits negative and rapidly decreasing photoconductivity upon light illumination followed by a gradual increase in conductivity. However, the negative photoconductivity persists for a test period longer than 30 hours when light is turned on and off. Adverse effects on electrical conductivity due to electron scattering by surface and interfacial charges, decrease in surface dopants due to desorption induced by incident photons, plasmonic coupling induced local electromagnetic fields combined with enhanced electron transport between silver nanoparticles, and photon generated electron-hole pairs in silicon contribute to the measured photoconductivity. Annealing by electrical current and Joule heating adds to the complexity of the observed effects of current density on positive and negative persistent photoconductivity.