  We find the admittance $Y(\omega)$ of a Josephson junction at or near a
topological transition. The dependence of the admittance on frequency and
temperature at the critical point is universal and determined by the symmetries
of the system. Despite the absence of a spectral gap at the transition, the
dissipative response may remain weak at low energies:
$\mathrm{Re}\,Y(\omega)\propto \max (\omega, T)^2$. This behavior is strikingly
different from the electromagnetic response of a normal metal. Away from the
critical point, the scaling functions for the dependence of the admittance on
frequency and temperature are controlled by at most two parameters.
