Carrier density and temperature-dependent resistivity of graphene grown by chemical vapor deposition (CVD) is investigated. We observe in low mobility CVD graphene device a generic insulating behavior at low temperatures, and eventually a metallic behavior at high temperatures, manifesting a nonmonotonic temperature dependent resistivity. This feature is strongly affected by carrier density modulation with the low-density samples exhibiting insulating-like temperature dependence up to higher temperatures than the corresponding high-density samples. To explain the temperature and density dependence of the resistivity, we introduce thermal activation of charge carriers in electron-hole puddles induced by randomly distributed charged impurities. Our observed temperature evolution of resistivity is then understood from the competition among thermal activation of charge carriers, temperature-dependent screening, and phonon scattering effects. Our experimental results are in good agreement with recent theories of graphene transport.