In ionic steady state, cells maintain different internal and external concentrations of various ionic species.
Cells are said to be in a steady state, NOT in an equilibrium. This means that there is a differential distribution of ions on either side of the cell membrane - that is, the amount of ions either side is not equal and therefore a charge separation exists. However, ions move across the cell membrane and almost constantly maintain a resting membrane potential; this is known as 'steady state.'
References
Steady state (biochemistry) Wikipedia(Text) CC BY-SA