Saudi news agency SPA citing official security sources said the policemen were injured in the explosion of an improvised bomb device.
The Monday incident followed the death of a soldier nearly two weeks ago after an army patrol was hit by a rocket-propelled grenade fired by gunmen in the same town. Five other soldiers were wounded in the attack.
Few days earlier, a Saudi child and a Pakistani worker were killed in an attack attributed to Shia militia.
Shia militants have been resisting construction projects in the town. Saudi authorities point out that they are razing the old town used by terrorists and gunmen as hideout for illegal activities including drug and arm dealing.
Authorities say old buildings will be replaced by shopping centres, office buildings and green spaces.
United Nations cultural experts slammed Riyadh last week over the razing of the town’s old quarter, saying the work erased cultural heritage and violated human rights, Reuters reports.
The town has been flashpoint between Saudi security forces and the Shia minority, which complains of marginalization. Riyadh muted protests in the area in 2011 as the Shia stood for more rights.
Tensions flared up following the execution of Shia cleric Nimr al-Nimr a year ago.