"He was attacked inside and outside a tent where he had been speaking," said Mohammed Saoud, who was with ex-MP Leith Shbeilat when Saturday's incident happened at Sakb in Jerash province some 50 kilometres (30 miles) north of Amman.
"Certain individuals threw stones at him and insulted him. He was not hurt." Shbeilat, an Islamist, is known for his forthright manner and criticism of the regime.
"I am astounded that people who call for reforms are considered critics of the regime," Shbeilat later said in an audio message posted on the Internet.
"If we call for a fight against corruption we are considered enemies of the regime. Does that mean the regime accepts corruption?" he asked.
"For 30 years, we have been trying to bring about reform, not the downfall of the regime. The problem is that the regime depends on people who actually undermine it," Shbeilat said in the recording.
The former parliamentarian under the reign of the late king Hussein has served several jail terms because of his political views. In October 2009, he was injured in an assault in the capital in broad daylight. An inquiry failed to uncover the identities of his attackers.
Saoud said Shbeilat had made an official complaint to Jerash police over the latest incident.