Actually not all the time, some times they just bounces around playfully playing cat and mouse (until they destruct in the most violent way known in the universe, bwahahahaha)
From Phys.Rev.A via Nature
Experimental evidence of antiproton reflection by a solid surface
A. Bianconi, et. al.
(Received 21 March 2008; revised 18 June 2008; published 11 August 2008)
We report here experimental evidence of the reflection of a large fraction of a beam of low energy antiprotons by an aluminum wall. This derives from the analysis of a set of annihilations of antiprotons that come to rest in rarefied helium gas after hitting the end wall of the apparatus. A Monte Carlo simulation of the antiproton path in aluminum indicates that the observed reflection occurs primarily via a multiple Rutherford-style scattering on Al nuclei, at least in the energy range 1–10 keV where the phenomenon is most visible in the analyzed data. These results contradict the common belief according to which the interactions between matter and antimatter are dominated by the reciprocally destructive phenomenon of annihilation.
Nice! But really it doesn't give as dramatic a phenomena for a good Dan Brown book. "He cut the eyeball out from the dead professor. With it he could get past the retina-scan security system and get to famed anti-matter, free-floating in a miniature magnetic coil. There it was the one and only store of anti-matter that had the potential to amuse the whole world by going boing! boing! boing!"... nah... doesn't work as well, not as dramatic.