Police official Nazir Ahmad said the bomb had been rigged to a motorcycle parked near the stage of the rally in the town of Jaaferabad.
He said some of the injured were in critical condition.
Ahmad said the injured belonged to the party of Nawab Akbar Bugti, who died on August 26, 2007, when a cave in which he was hiding collapsed during a military operation against him in the southwestern Baluchistan province.
Bugti was a former Baluchistan governor and had led a violent campaign to pressure the central government to give his impoverished province a larger share of money from oil and gas extracted from there.