The transient electrical behavior of an electrode/electrolyte interface based on an electrode micro-structured with gold protruding mushroom shapes is measured and modeled. The application of a voltage pulse train with changing frequency generates a corresponding train of current pulses with an offset current that approaches a saturation limit exponentially. The transient behavior of the electrical current was accurately reproduced using the Nernst-Planck-Poisson model and the geometric parameters of the mushroom shape. Spatiotemporal patterns of the electric field demonstrate that the current transient is caused by a slow kinetics of charges accumulating at the gold/electrolyte interface and under the micro-mushroom cap. The accumulation of charges establishes an internal electrical potential that drives a Faradic current through the mushroom/electrolyte interface. The aim of this work is to understand how this charge dynamics in the vicinity of the three-dimensional electrode surfaces is established and how it can be minimized to prevent damage to cells and tissues under electrical stimulation.