Thanks @stuck? for this one
DICE has recently announced that you will be able to carry forward your Battlefield 4 stats from the PS3 console over to the PS4 (if you should purchase one).
You will not have to restart your level up process when the game is released on PS4 in the comings months.
However, if you need to buy another copy of the game to play on PS4 if you already own it for the PS3 is another story not yet being told.