We have discovered oscillations in a highly ionized potassium plasma of non-uniform density in a magnetic field of an intensity of 600–1600 Oe and observed three or four harmonics with a fundamental frequency of ∼5–10kHz.The oscillations represent an azimuthal wave having a component along the magnetic field. Oscillation frequency is inversely proportional to the magnetic field strength. Oscillations are observed both in a dilute (n = 108–109 cm–3), and in a dense plasma (n = 1010–5 × 1011cm–3). Oscillation excitation is not related to the presence of electric layers on the plasma boundary.It is shown that the observed oscillations are the development of "universal" instability of a plasma of non-uniform density.