  The physical origin of fast radio bursts (FRBs) remains unclear. Finding
multiwavelength counterparts of FRBs can be a breakthrough in understanding
their nature. In this work, we perform a systematic search for astronomical
transients (ATs) whose positions are consistent with FRBs. We find an
unclassified optical transient AT2020hur ($\alpha=01^{\mathrm{h}}
58^{\mathrm{m}} 00.750^{\mathrm{s}} \pm 1$ arcsec, $\delta=65^{\circ}
43^{\prime} 00.30^{\prime \prime} \pm 1$ arcsec) that is spatially coincident
with the repeating FRB 180916B ($\alpha=01^{\mathrm{h}} 58^{\mathrm{m}}
00.7502^{\mathrm{s}} \pm 2.3$ mas, $\delta=65^{\circ} 43^{\prime}
00.3152^{\prime \prime} \pm 2.3$ mas). The chance possibility for the
AT2020hur-FRB 180916B association is about 0.04%, which corresponds to a
significance of $3.5\sigma$. We develop a giant flare afterglow model to fit
AT2020hur. Although the giant flare afterglow model can interpret the
observations of AT2020hur, the derived kinetic energy of such a GF is at least
three orders of magnitude larger than that of the typical GF, and there is a
lot of fine tuning and coincidences required for this model. Another possible
explanation is that AT2020hur might consist of two or more optical flares
originating from the FRB source, e.g. fast optical bursts produced by the
inverse Compton scattering of FRB emission. Besides, AT2020hur is located in
one of the activity windows of FRB 180916B, which is an independent support for
the association. This coincidence may be due to the reason that the optical
counterpart is subject to the same periodic modulation as FRB 180916B, as
implied by the prompt FRB counterparts. Future simultaneous observations of
FRBs and their optical counterparts may help reveal their physical origin.
