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 ($1sigma$). 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 ($-1.88pm0.15$) and the characteristic timescale ($tau_{rm br}equiv 1/(2pi f_{rm br})=1.4_{-0.5}^{+1.9},$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.
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