We analyze the diffusion process of rigid homonuclear dimers (AA) adsorbed on a simple cubic (sc(100))surface. The coverage dependence of the collective diffusion coefficient is obtained by means of Monte Carlo simulations in the framework of the Kubo-Green formalism. Different microscopic diffusion mechanisms are introduced and their influence in the collective motion have been investigated. Repulsive adsorbate-adsorbate interaction, J A A , is considered in order to analyze the influence of such parameter on the diffusion process. The behavior of the diffusion coefficient in the critical region is studied, where several ordered adsorbate structures appear depending on the values of J A A .