This paper presents an open-loop balance control for an active leg exoskeleton based on human balance strategies, and how the machine can balance itself according to perturbations. The control is designed to balance the exoskeleton with a view to assist a well and able operator that leads the movements of the coupled system {operator+exoskeleton}. It is inspired by biomechanic works showing that human balance relies on three strategies : the displacement of the center of mass, the contribution of each leg to produce efforts and stepping. We assimilate the exoskeleton to a Linear Inversed Pendulum model to describe its global behavior, and we use its capture point to identify a loss of balance situation possibly caused by the operator and adapt the reaction of the machine. Thanks to capture point's dynamics regarding to the center of mass and the center of pressure, we are able to control the machine and bring it back into a stable situation.