This is a typical human walking posture as can be seen in the monk image comparisons provided. If this was just a rock it would fall over at this angle as the centre of gravity looks quite high.
It could be a figurine carved in stone perhaps but it would still topple over unless fixed to the rock below.
Estimated height, 1.5 - 3 feet. (Approx)
"I was actually looking for another fence post (as seen in my previous video) when I spotted this guy that looks as if he is climbing the hill towards Mount Sharp, but he has not moved so may be a statue/figurine that is fixed to the rock below".
NASA image link: http://www.gigapan.com/gigapans?query=sol+590
UPDATE - The same figure can be seen in this Sol 592 image on the centre left so must be a statue/figure. http://mars.jpl.nasa.gov/msl/multimedia/raw/?rawid=0592ML0024920250300840E01_DXXX&s=592
Also here on Sol 589: http://mars.jpl.nasa.gov/msl/multimedia/raw/?rawid=0589ML0024760010300600E01_DXXX&s=589