We describe 3D resistive magnetohydrodynamic (MHD) numerical experiments at a null point driven by the rotation of magnetic field lines near the spine of the null. When field lines around the spine are rotated, a twist wave propagates toward the null along field lines, satisfying a Klein--Gordon equation. While the helical Alfv¿n wave spreads out as the null is approached, a fast-mode wave focuses on the null and wraps around it. Only a weak diffusion of the twisted field line structure is found to take place.