Data on the damping spectra of commercial poly(methyl methacrylate) (PMMA) are reported, both at low (of the order of 1 Hz) and at intermediate (of the order of 50 Hz) frequencies. It is shown that the damping does not only depend strongly on temperature and frequency but also on the strain amplitude applied to the specimen. In other words, the dynamic mechanical behavior of PMMA is nonlinear and cannot be described in terms of linear viscoelasticity. Finally, some aging effects in the damping, measured at low frequencies, are also reported.