On Friday, the main Shia Muslim opposition group warned the Sunni-led authorities that any attempt to rig the parliamentary and municipal polls would be opposed.
Hundres of men and women had queued waiting for the polling stations to open at 8am (0500 GMT).
About 295,000 voters are entitled to elect 39 MPs in an equivalent number of constituencies. There are a total of 207 candidates, including 17 women.
One seat in the 40-strong chamber has already gone to Latifa al-Qouhoud, a woman who stood unopposed in her constituency, making her the first female member of parliament in the kingdom's history.
The Islamic National Accord Association (INAA), which is the major Shia formation in the kingdom, is fielding 17 candidates, while the left-leaning National Democratic Action Association has presented six candidates.
