  We performed systematic AC susceptibility and magnetic moment measurements to
investigate the vortex dynamics and pinning in the $EuRbFe_4As_4$ single
crystal as a function of temperature, frequency, and DC magnetic field. The
vortex solid-liquid line was determined and it fits well with
$H(T_p)=H_0(1-t_p)^\beta$ using $\beta$=1.74-1.91, for $H\parallel ab$. It
indicates a rather high pinning strength of the vortex system. The activation
energy $U_0$ was determined from thermally activated flux creep theory and
reached 6700 K at low fields, suggesting strong vortex pinning. A field
dependence of $U_0(H\parallel ab)\sim H^a$ with $a=0.47$ suggests thermally
activated plastic pinning or caused by planar defects. Magnetic moment
measurements also confirmed strong pinning in a $EuRbFe_4As_4$ superconductor
and the superconducting response gives the main contribution to the $M(H)$
hysteresis. Additionally, we found evidence of long-range magnetic interactions
in $Eu^{2+}$ sublattice and the FM-like nature of $Eu^{2+}$ atoms ordering.
