The Saudi authorities say they have detained 136 suspected militants, including a potential suicide bomber.
The arrests were made over the past few months in several cities, and those held include members of al-Qaeda-type cells, the interior ministry said.
A ministry spokesman told the BBC that 115 of the suspects were Saudi nationals - the rest were foreigners.
They are accused of planning to bring down the Saudi royal family and attack Western targets.
Militants began a campaign in Saudi Arabia in 2003 with attacks on Western housing compounds.
However violence has declined in recent years in the face of tough security measures.
The only known attempted operation by Islamic militants this year was a foiled attack against the country's largest and most important oil facility.
The interior ministry spokesman, General Mansoor al-Turki, said some of the militant groups had been about to carry out attacks in Saudi Arabia while others were still in the preparatory stages.
He said the authorities had withheld the announcement of the arrests until all the suspects had been rounded up.
"We're talking about eight different cells that were caught all over the kingdom, in almost all areas," Mr Turki told the BBC.
Some of those arrested were recruiting others to fight in "unstable countries", he added.
Others were allegedly recruiting militants to be trained abroad and then sent back to Saudi Arabia to carry out attacks.