  Quasi-periodic oscillation (QPO) detected in the X-ray radiation of black
hole X-ray binaries (BHXBs) is thought to originate from dynamical processes in
the close vicinity of the black holes (BHs), and thus carries important
physical information therein. Such a feature is extremely rare in active
galactic nuclei (AGNs) with supermassive BHs. Here we report on the detection
of a possible X-ray QPO signal with a period of 3800\,s at a confidence level
$>99.99\%$ in the narrow-line Seyfert 1 galaxy (NLS1) 1H~0707-495 in one data
set in 0.2-10\,keV taken with {\it XMM-Newton}. The statistical significance is
higher than that of most previously reported QPOs in AGNs. The QPO is highly
coherent (quality factor $Q=\nu/\Delta\nu \geqslant 15$) with a high rms
fractional variability ($\sim15\%$). A comprehensive analysis of the optical
spectra of this AGN is also performed, yielding a central BH mass
$5.2\times10^6\,M_{\odot}$ from the broad emission lines based on the scaling
relation. The QPO follows closely the known frequency-BH mass relation, which
spans from stellar-mass to supermassive BHs. The absence of the QPO in other
observations of the object suggests it a transient phenomenon. We suggest that
the (high-frequency) QPOs tend to occur in highly accreting BH systems, from
BHXBs to supermassive BHs. Future precise estimation of the BH mass may be used
to infer the BH spin from the QPO frequency.
