Antiferromagnetic resonance in RbMnF3, with the magnetization in the flopped state, has been reported previously. This paper reports an investigation of resonance for the low-field region 0–5000 Oe. For applied fields less than about 3000 Oe, the static equilibrium position of the sublattice magnetizations is in general multivalued, due to the cubic anisotropy. Experimental results are presented which show the resonance, at 4.2°K, as a function of magnitude and direction of the applied field with respect to the cubic lattice. A theory of antiferromagnetic resonance for cubic materials is also presented. With appropriate choice of coordinates, the linearized equations of motion permit the normal mode frequencies to be derived. By considering the magnetization to be locally uniform, and confining the applied field to a symmetry plane, solution of the static equilibrium problem has been obtained. The model has been used in conjunction with the resonance analysis to calculate the resonant frequencies. There is good agreement between theory and experiment for some of the observed resonances.