  We experimentally study a periodically driven many-body localized system
realized by interacting fermions in a one-dimensional quasi-disordered optical
lattice. By preparing the system in a far-from-equilibrium state and monitoring
the remains of an imprinted density pattern, we identify a localized phase at
high drive frequencies and an ergodic phase at low ones. These two distinct
phases are separated by a dynamical phase transition which depends on both the
drive frequency and the drive strength. Our observations are quantitatively
supported by numerical simulations and are directly connected to the change in
the statistical properties of the effective Floquet Hamiltonian.
