  We study the supercurrent decay of a Bose-Einstein condensate in a ring trap
combined with a repulsive barrier potential. In recent experiments, Kumar {\it
et al.} [Phys. Rev. A {\bf 95}, 021602(R) (2017)] have measured the dependence
of the decay rate on the temperature and the barrier strength. However, the
origin of the decay observed in the experiment remains unclear. We calculate
the rate of supercurrent decay due to thermally activated phase slips (TAPS) by
using the Kramers formula based on the Gross-Pitaevskii mean-field theory. The
resulting decay rate is astronomically small compared to that measured in the
experiment, thus excluding the possibility of TAPS as the decay mechanism.
Alternatively, we argue that three-body losses can be relevant to the observed
decay and predict that one can observe supercurrent decay via TAPS by
decreasing the number of atoms.
