Is playing poker on facebook allowed (just for fun, there is no use of real money)?

There is a scholarly disagreement over this issue. There is no objection to playing this game so long as it does not include gambling; does not distract a Muslim from making remembrance of Allah [dhikr] and observing the legal obligations; and does not arouse grudges among players involved.
However, if this game involves money [gambling], it is then deemed prohibited [haram].