  We discuss the possible source of a highly-dispersed radio transient
discovered in the Parkes Multi-beam Pulsar Survey (PMPS). The pulse has a
dispersion measure of $746\mathrm{cm}^{-3}\mathrm{pc}$, a peak flux density of
400 mJy for the observed pulse width of 7.8 ms, and a flat spectrum across a
288-MHz band centred on 1374 MHz. The flat spectrum suggests that the pulse did
not originate from a pulsar, but is consistent with radio-emitting magnetar
spectra. The non-detection of subsequent bursts constrains any possible pulsar
period to $\gtrsim1$ s, and the pulse energy distribution to being much flatter
than typical giant pulse emitting pulsars. The burst is also consistent with
the radio signal theorised from an annihilating mini black hole. Extrapolating
the PMPS detection rate, provides a limit of
$\Omega_{BH}\lesssim5\times10^{-14}$ on the density of these objects. We
investigate the consistency of these two scenarios, plus several other possible
solutions, as potential explanations to the origin of the pulse, as well as for
another transient with similar properties: the Lorimer Burst.
