Boycotts and political demonstrations are not uncommon to Peshawar. They happen quite regularily and can have so many supporters that the entire downtown area would be shut off to vehicles. The places where these happen most are: High Courts, Qissa Khwani Bazaar, GT Road. In every case, police attend these rallies and set up barbed-wire rolls along the streets to prevent people from entering. Of course there are instances of suicide bombers at rallies, and it's best to avoid them as much as you can.
My father-in-law (a native of Peshawar) works in the Old City, and when there is news of a demonstration in the downtown area, he takes the entire day off work... it is more worth it to him to lose a day's worth of pay than risk getting caught in the middle of things.
Contrary to common opinions Peshawar is a relatively calm and peaceful place. But every now and then you would encounter demonstrations against Western policies that might turn violent. In these cases stay away from public places as much as possible, especially as a Westener.
I snapped this beauty right before I ducked into a shop. This was a completely non-violent protest. One of the issues deals with a huge Dam going up nearby being built by an American company. I never hid that I was an American in Pakistan, and was always well received (to my face anyway)