Abdullah al-Qallaf was martyred on Monday while driving in his car in the town of al-Awamiyah.
According to local reports, Qallaf was mistakenly shot by Saudi troops who were targeting a political activist.
Following the incident Saudi forces removed Qallaf body to a undisclosed location.
The Shia-populated 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. Security forces have increased security measures across the province.
Over the past years, Riyadh has also redefined its anti-terrorism laws so as to also target activism.