  We report nuclear quadrupole resonance (NQR) studies on the chain Cu sites of
PrBa$_{2}$Cu$_{4}$O$_{8}$, a quasi-one-dimensional conductor with a nearly
quarter-filled band. The nuclear spin-lattice relaxation rate $1/T_{1}$ shows a
pronounced peak near 100 K caused by fluctuations of electric field gradient
(EFG). Similar peak was observed for the spin-echo decay rate $1/T_{2}$,
however, at a different temperature near 50 K. These results and broadening of
the NQR spectrum at low temperatures indicate that slow charge fluctuations of
either electronic or ionic origin freeze gradually at low temperatures.
