This paper concerns the analysis of the interaction force among the permanent magnets (PM) in a Halbach array as used in a moving-magnet planar actuator. The goal is to analyze the magnitude of these forces and to what extent the mechanical construction of an aluminium plate, on which the permanent magnets are mounted, is deformed by the interaction force among the permanent magnets. The interaction forces are obtained from analytical models which have been verified with an electromagnetic Finite Element Method (FEM) simulation. These results are used in a mechanical FEM simulation to determine the deformation of the magnet assembly.