Brake blocks too close to wheel rims. Screw the adjuster on cable or brake IN to achieve small gap between blocks and rim (1-2mm or so) . If you can't achieve that either the cable slack needs adjusting slightly by loosening the cable grip screw - then readjust the tensioner.

Or - the brake is off centre if it's the sort of brake that can go off centre and the blocks are rubbing. Just make sure you do the cable grip screw up properly if you loosen it.

Brakes shouldn't rub - full stop.