We prove the existence of at least one non-decreasing sequence of positive eigenvalues for the problem, $$\begin{gathered}\left\{ \begin{array}{ll} \Delta_{p(x)}^{2}u-\triangle_{p(x)}u= \lambda |u|^{p(x)-2}u, \ \ \quad in \ \Omega \\ u\in W^{2,p(x)}(\Omega)\cap W_{0}^{1,p(x)}(\Omega),\end{array}\right. \end{gathered}$$ Our analysis mainly relies on variational arguments involving Ljusternik-Schnirelmann theory.