Anomalous transport behaviour, i.e. the dependence of the tunnel resistance on the injection current, has been discovered in Ta/Co/Al2O3/FeNi tunnel junctions. The zero-field voltage-current characteristic of the magnetic tunnelling junction obeys the transport principle of the normal tunnel junction at low injection current, but it exhibits a negative resistance behaviour when the injection current is raised to the break-over current level. The physics of the restorable electric breakdown has been initially studied.