  We report the discovery of a highly luminous optical transient (OT), SDSS
J124602.54+011318.8, associated with a galaxy at a redshift of 0.385. In this
paper we consider the possibility that the OT may be a GRB afterglow. Three
sets of images and two sets of spectra were obtained as part of the normal
operations of the Sloan Digital Sky Survey (SDSS). In the first two image sets,
observed two nights apart, the object appears as a point source at
$r^{*}\approx 17$. The third image set, observed about 410 days later, shows an
extended source which is more than 2.5 magnitudes fainter. The spectra were
observed about 400 and 670 days after the first two image sets, and both show
an apparently normal galaxy at a redshift of 0.385. Associating the OT with the
galaxy, the absolute magnitude was $M_{r^*}=-24.8$, which is over 4 magnitudes
brighter than the most luminous supernova ever measured. The spectral energy
distributions of the galaxy-subtracted OT derived from the first two image sets
are well-fit by single power-laws with indices of $\beta_{\nu}=-0.92$ and -1.29
respectively, similar to most GRB afterglows. Based upon the luminosity of the
OT, non-detections in contemporaneous ROTSE-I images, and the change in
spectral slope, the OT, if an afterglow, was likely discovered early during a
``plateau'' or slowly-fading phase. The discovery of a GRB afterglow at this
stage of the SDSS is consistent with expectations, but only if the optical
emission is much less strongly beamed than the gamma-rays. We emphasize that
other explanations for the OT cannot be ruled out; a recent follow-up study by
[galyam02] provides strong evidence that this source is in fact an unusual AGN.
