Observed time-varying properties of the Earth’s crust before and after large earthquakes are correlated with the increase in stress. Co- and postseismic slip of the great earthquakes can give rise to temporal changes in the medium either due to strong ground motion damaging near-surface sediment layer or stress perturbations modulating crack density and/or fluid movement at depth. Such time-varying crustal properties can result in a fractional change in seismic wave attenuation and velocity. The spatial and temporal variations of coda attenuation (Qc) were studied in the source region of the Ahar-Varzaghan (Mw 6.5, 2012) earthquake. The Qc values were determined from the amplitude decay rate of the S-wave coda in narrower overlapping frequency bands in the range f=1–24 Hz using different lapse time windows from 10 to 40 s, based on a single back-scattering model for regional earthquakes recorded in a period from February 2012 to January 2013, including pre- and postseismic period. We found that the value of Qc increases 11 days before mainshock and decreases after that. Temporal changes in Qc in this earthquake imply variations of crack density and pore-fluid saturation in the ruptured fault zone. The reduction in Qc following this event indicates high pore fluid saturation within the fractured fault zone due to the postseismic fluid redistribution. Approaching the earthquake, we observed clear variations in the seismic wave propagation properties. The elastic properties of rocks in the fault region underwent a sharp change before the earthquake. From our observations, we infer that a complex sequence of dilatancy-diffusion processes takes place and that fluids play a key role in the fault failure process.