The northern Zagros area in western Iran experiences high seismic activity. In this research, we investigated how shear waves attenuate in this region using the non-parametric generalized inversion technique (GIT). GIT is a data-driven method that separates the different contributions (path, site, and source effects) influencing the recorded ground motion's Fourier amplitude spectra (FAS). The attenuation function in the non-parametric scheme is not predefined (it is only required to be a smooth distance function). This allows assessing the potential complexity of attenuation characteristics without imposing a priori parametric model. We analyzed 2,699 waveforms recorded at hypocentral distances between 10 and 150 km from 228 strong-motion stations of the Iran Strong Motion Network (ISMN). We utilized data from 1,563 local events with moment magnitudes ranging from 3.0 to 7.3 Mw. We computed the Fourier amplitude spectra of acceleration time-series in the 0.1–30 Hz frequency range. The evaluated non-parametric attenuation functions decayed uniformly with distance across the entire frequency range. We performed 100 bootstrap GIT inversions at each frequency and calculated the mean and standard deviation to assess the stability of the inversion results. The quality factor of S waves and the frequency-dependent geometrical spreading were estimated simultaneously by regression to the non-parametric attenuation function in the 10-110 km distance range. We considered 10 km as the reference distance (R0), where the attenuation function equals unity. The corresponding frequency-dependent quality factor was Q_s (f)=165f^0.64 in the 0.5-25 Hz frequency range. This S-wave quality factor model agrees with values for tectonically active regions and previous Zagros studies. The geometrical spreading increased for frequencies above 10 Hz. This result can improve the accuracy of ground motion models (GMMs) used for seismic hazard assessment in the region (Amiri Fard et al., 2019; Sadeghi-Bagherabadi et al., 2020). Overall, the study provides valuable insights into shear wave attenuation in northern Zagros. It highlights using non-parametric techniques like GIT to better understand complex attenuation without imposing parametric models. The findings can inform future research and monitoring efforts in this seismically active area.