It's unlikely to go into Mars orbit, unless they have hidden a bunch of thrusters in there to slow it down to get captured by Mars' gravity. More likely it will be in a permanent Sun-centric orbit with the distance to Mars as the aphelion (furthest point from Sun) and Earth's orbit as the perihelion (nearest point to Sun). Either that or it will get close to Mars and get a Voyager-style gravity assist to the outer Solar System.
Should also say that we are not at the ideal point in the Earth and Mars' orbits to do a transfer anyway, although I think the FH has enough spare payload mass to make up for that (note - speculation, I haven't worked this out. Edit: Elon just confirmed it
Elon Musk on Twitter ), but my money would be on the former statement above.