  We report experimental studies of the low frequency electrodynamics of
ZrB$_{12}$ and Nb single crystals. AC susceptibility at frequencies 3 - 1000 Hz
have been measured under a dc magnetic field, $H_0$, applied parallel to the
sample surface. In the surface superconducting state, for several $H_0$, the
real part of the ac magnetic susceptibility exhibits a logarithmic frequency
dependence as for spin-glass systems. Kramers-Kronig analysis of the
experimental data, shows large losses at ultra low frequencies ($<3$ Hz). The
wave function slope at the surface was found. The linear response of the order
parameter to the ac excitation was extracted from the experimental data.
