This work reports the observation of strong thermally transferred optically stimulated luminescence (TT-OSL) signal of BeO OSL ceramic detectors. If the detector is irradiated and the OSL signal is measured for a prolonged time (bleached), subsequent OSL measurements result in zero signal. If the same detector, however, is heated to temperatures in the 225–335 °C range (at 5 °C/s), subsequent OSL measurements at room temperature result in an intense signal, even without additional irradiation. The TT-OSL is maximum for a pre-heating to 275 °C (if heated linearly at 5 °C/s), reaching a value of 56 % of the original OSL signal. Both OSL and TT-OSL are reproducible (∼3 % standard deviation) and linear with dose over the dose range investigated (up to 100 mGy). The shape of the OSL and TT-OSL curves are essentially identical. A possible explanation for this phenomenon is the thermally stimulated transfer of trapped charges from optically inactive traps to optically active traps responsible for the OSL signal. Correlation between the OSL, TT-OSL and the thermoluminescence (TL) peaks suggests the trapping centers associated with the TL peak at ∼310 °C/s (at 5 °C/s) as the source of the trapped charges. These results have implication for the re-estimation of the OSL signal in BeO detectors accidentally exposed to light. They not only provide further evidence that the material is not completely reset simply by bleaching (optical stimulation), but also open a new line of investigation into the underlying TL/OSL mechanisms in BeO.