Local sources, requesting anonymity, said security forces stormed into Sanabes village of Tarout Island on Saturday afternoon, triggering an exchange of gunfire with local residents.
The sources added that two distinguished opposition figures were fatally shot in the process.
According to Reuters, eight people were killed during the heavy crackdown.
Saudi Arabia has stepped up what appears to be politically-motivated arrests, prosecution and conviction of peaceful dissident writers and human rights campaigners.
Eastern Province has been the scene of peaceful demonstrations since February 2011. Protesters have been demanding reforms, freedom of expression, the release of political prisoners, and an end to economic and religious discrimination against the oil-rich region.
The protests have been met with a heavy-handed crackdown by the regime, with regime forces increasing security measures across the province.
Over the past years, Riyadh has also redefined its anti-terrorism laws to target activism.
In January 2016, Saudi authorities executed Shia cleric Sheikh Nimr Baqir al-Nimr, who was an outspoken critic of the Riyadh regime. Nimr had been arrested in Qatif, Eastern Province, in 2012.