The crowd apparently tried to attack a police station near the central Earth Roundabout.
Reports say several people were injured in clashes with police.
According to witnesses, police subsequently withdrew and the army moved in. Roadblocks have also been set up on the main road to the capital, Muscat.
It's the second day protesters have rallied in Sohar. Protests were also taking place in the southern town of Salalah.
Oman's Sultan Qaboos bin Said reshuffled his cabinet on Saturday in a bid to quell public demand for political reforms.
A week earlier, around 300 people carried out a peaceful demonstration in Muscat, demanding more jobs, better salaries and measures to curb corruption.