We present a numerical model for binary fluid mixtures. Our hybrid approach combines the lattice Boltzmann method for solving the Navier-Stokes equation and a finite difference scheme for the convection-diffusion equation. The equilibrium properties of the system are controlled via a free-energy functional to properly calculate the pressure tensor of the system. The latter enters the Navier-Stokes equation via a forcing term in the lattice Boltzmann method. This method allows to improve some analytical and numerical issues of previous formulations. We derive the continuum limit of the model through a Chapman-Enskog expansion. Some numerical results to test the method are presented.