We performed measurements of the magnetic response of a single mesoscopic ring made of a GaAlAs/GaAs heterojunction (2 DEG). We detected a magnetic signal, with a period h/e, which is an evidence, of persistent currents. The amplitude and the sign of this signal seem to vary in time despite a stable amplitude and phase of the Aharonov-Bohm conductance oscillations. We discuss the improvements necessary to determine the nature of these variations.