Summary: We consider solving a generalized Allen-Cahn equation coupled with a passive convection for a given incompressible velocity field. The numerical scheme consists of the first order accurate stabilized implicit explicit time discretization and a fourth order accurate finite difference scheme, which is obtained from the finite difference formulation of the \(Q^2\) spectral element method. We prove that the discrete maximum principle holds under suitable mesh size and time step constraints. The same result also applies to the construction of a bound-preserving scheme for any passive convection with an incompressible velocity field.