We have found a chaotic regime of counter-motion of the normal and superfluid magnetizations in3He-B. It takes place under conditions corresponding to the experiments with “catastrophic” relaxation. We study a spatially homogeneous regime of the magnetization's precession by employing a numerical simulation of the Leggett-Takagi theory, and show that there is a topological reconstruction of the spin dynamics that brings about a chaotic regime of Arnold diffusion. It is important that the regime, which takes place owing to the sophisticated nature of the Leggett-Takagi equations, does not require an external driving force.