In the present paper, the characteristics of low‐frequency stable damping are studied in a multiphase eutectoid Al‐Zn alloy. Experimental results show that, within a low‐temperature and low‐strain‐amplitude range, the damping evidently manifests itself by linear viscous characteristics, namely, it obeys a lawQ−1=(B/fn)exp(−nH/kT), whereHis the real process activation energy,Bandn(=0.21) are two experimental parameters, andkis the Boltzmann constant. A value ofH=0.74 eV is obtained, which is closely related to the viscosity during interface motion. Accordingly, a linear viscous interface motion mode is put forward and can explain the experimental results as well.