Some do, some don't.
It depends by the type of the aircraft and by the need to see behind the aircraft itself.
Just as an example, this is a render of a Boeing F/A-18E "Super-Hornet" cockpit:
On the canopy's frame are located three adjustable mirrors (like the one on the windshield of a car) the pilot can use to see what's happening behind him.
As already stated in comments, aircraft usually don't "power-back" and there is no overtaking like in cars (where cars from behind can overtake you just from left or right), so usually there is no need of mirrors inside a cockpit.
In a military aircraft, mirrors increase your situational awareness, but
- with a wide Field-of-View (FoV), details or a distant aircraft or missile cannot be seen
- with a narrow FoV, a smaller portion of the sky is visible
Just for reference, the F-16 or the F-22, both featuring a single piece canopy, don't have rear view mirrors. The pilot must turn the head as much as he/she can and look behind.