  Magnetization measurements under hydrostatic pressure up to 10.5 kbar in
zirconium dodecaboride ZrB$_{12}$ superconductor ($T_c\simeq6.0$ K at $p=0$)
were carried out. A negative pressure effect on $T_c$ with ${\rm d} T_c/{\rm d}
p =-0.0225(3)$ K/kbar was observed. The electron-phonon coupling constant
$\lambda_{el-ph}$ decreases with increasing pressure with ${\rm
d}\ln\lambda_{el-ph}/{\rm d}p\simeq-0.20$%/kbar. The magnetic field penetration
depth $\lambda$ was studied in the Meissner state and, therefore, probes only
the surface of the sample. The absolute values of $\lambda$ and the
superconducting energy gap at ambient pressure and zero temperature were found
to be $\lambda(0)=$140(30) nm and $\Delta_0=$1.251(9) meV, respectively.
$\Delta_0$ scales linearly with $T_c$ as $2\Delta_0/k_BT_c=4.79(1)$. The
studies of the pressure effect on $\lambda$ reveal that $\lambda^{-2}$
increases with pressure with ${\rm d}\ln\lambda^{-2}(0)/{\rm d}p=0.60(23)$
%/kbar. This effect can not be explained within the framework of conventional
adiabatic electron-phonon pairing, suggesting that close to the surface, an
unconventional {\it non-adiabatic} character of the electron-phonon coupling
takes place.
