We have carried out experimental investigations of the increased diffusion of a low-temperature plasma across the lines of force of a constant homogeneous magnetic field under conditions of high-frequency heating for a frequency approaching ion cyclotron frequency. The plasma was created in a glass tube by a pulse discharge with oscillating electrons in hydrogen at a pressure range of 5 × 10−4–5 × 10−2 torr. Initial plasma density exceeded 1.7 × 1013 cm−3. A high-frequency electric field with a frequency of 7.45 × 106 Hz and an axial period of 23 cm was excited in the plasma by an alternating current flowing along a spiral surrounding the discharge tube. The spiral and the capacitors connected to it formed an artificial line that was fed from the pulse generator with self-excitation. In the region of magnetic fields where there occurs a strong absorption of highfrequency energy by the plasma caused by ion cyclotron resonance time of plasma decay decreases sharply if the amplitude of the high-frequency current in the spiral exceeds some critical value depending on neutral gas pressure. Here ion diffusion across the magnetic field lines increases and chaotic oscillations arise in the plasma. It has been ascertained in experiments that for neutral gas pressures exceeding 10−2 torr the ratio between the critical current value and the pressure remains constant. On these grounds the assumption was made that anomalous diffusion arises when the ion drift velocity under the effect of an alternating azimuthal electric field exceeds a critical value. This is possibly associated with the appearance of "flute" instability. The possibility for flute instability to arise is apparently confirmed also by this fact: as is shown by evaluation, the velocity gained by the ion between two collisions in an azimuthal electric field for a current approaching a critical current equals in order of magnitude thermal ion velocity. We note that the investigated phenomenon of anomalous plasma diffusion in ion cyclotron resonance can be the reason for increased velocity of plasma decay in all devices in which the phenomenon of strong damping of an ion cyclotron wave in the region of ion cyclotron resonance is used for plasma heating and where considerable high-frequency powers are introduced into the plasma.