We consider the set of all almost Kähler structures (g,J) on a 2n-dimensional compact orientable manifold M and study a critical point of the functional ${ℱ}_{\lambda ,\mu }(J,g)={\int }_M(\lambda \tau +\mu \tau *)d{M}_g$ with respect to the scalar curvature τ and the *-scalar curvature τ*. We show that an almost Kähler structure (J,g) is a critical point of ${ℱ}_{-1,1}$ if and only if (J,g) is a Kähler structure on M.