In this paper we discuss the existence of prescribed mean curvature (PMC) graphs with fixed graphical boundaries in the product manifold N×R. We define an Nc-f domain in which closure does not contain certain domains with the mean curvature of its boundary equal to f . We show the existence of corresponding PMC graphs over bounded Nc-f domains with natural boundary conditions via a blow-up method from Schoen-Yau. This existence can be used in the Plateau problem of PMC surfaces in 3-manifolds.