  We present optical light curves from the Transiting Exoplanet Survey
Satellite (TESS) for the archetypical dwarf active galactic nucleus (AGN) in
the nearby galaxy NGC 4395 hosting a $\sim 10^5\,M_\odot$ supermassive black
hole (SMBH). Significant variability is detected on timescales from weeks to
hours before reaching the background noise level. The $\sim$month-long, 30
minute-cadence, high-precision TESS light curve can be well fit by a simple
damped random walk (DRW) model, with the damping timescale $\tau_{\rm DRW}$
constrained to be $2.3_{-0.7}^{+1.8}$~days ($1\sigma$). NGC 4395 lies almost
exactly on the extrapolation of the $\tau_{\rm DRW}-M_{\rm BH}$ relation
measured for AGNs with BH masses that are more than three orders of magnitude
larger. The optical variability periodogram can be well fit by a broken power
law with the high-frequency slope ($-1.88\pm0.15$) and the characteristic
timescale ($\tau_{\rm br}\equiv 1/(2\pi f_{\rm br})=1.4_{-0.5}^{+1.9}\,$days)
consistent with the DRW model within 1$\sigma$. This work demonstrates the
power of TESS light curves in identifying low-mass accreting SMBHs with optical
variability, and a potential global $\tau_{\rm DRW}-M_{\rm BH}$ relation that
can be used to estimate SMBH masses with optical variability measurements.
