The stability of co-orbital motions is investigated in such exoplanetary systems, where the only known giant planet orbits in the habitable zone. If the regions of the triangular Lagrangian points are stable, they are possible places for additional smaller planets. We determine the stability properties of these regions by using numerical methods, the relative Lyapunov indicators and long time numerical integrations. Stability maps in the initial synodic longitude - semi-major axis plane are derived, and their dependence on the mass ratio and the orbital eccentricity of the giant planet is analysed.