Awad al-Qarni, previously accused of having links to the Muslim Brotherhood, which is banned in Saudi Arabia, was also fined 100,000 riyals ($27,000), Okaz newspaper reported on its website late on Thursday.
In September, Qarni condemned a US law that allowed the families of the victims of September 11 attacks to sue Saudi Arabia in a series of tweets, calling on Riyadh to withdraw investments worth billions of dollars from the US and seek alternative sources of armaments.
He has also been embroiled in several twitter controversies, including a row with a supporter of Yemen's Houthi rebels who allegedly popularised a hashtag claiming Qarni was planning to assassinate the Saudi king.
The ruling did not name the "famous preacher" but Qarni himself confirmed the verdict - by tweeting on his @awadalqarni Twitter account.
"I am prevented from writing" on the account, he wrote, before issuing a Twitter message early on Friday thanking his followers.
Qarni was "one of the key clerics of the Sahwa movement", British scholar Toby Matthieson has written.
The Sahwa emerged in Saudi Arabia in the 1960s and 1970s as "a modern form of Islamic activism" which had wide impact and whose founders were exiled Brotherhood members, according to another expert, Stephane Lacroix.
|Qarni was 'one of the key clerics of the Sahwa movement,' British scholar Toby Matthieson has written|
Saudi Arabia, Egypt and the United Arab Emirates have all declared the Muslim Brotherhood to be a "terrorist group".
Okaz said Riyadh's Specialised Criminal Court, which handles "terrorism" cases, convicted the preacher on Thursday of spreading content on Twitter which "could jeopardise public order and provoke public opinion".
It said the content "could affect the relationship of the people with the leadership, and the relationship of Saudi Arabia with other countries".
There were no further details but Okaz said Qarni was tried without having been arrested.
"We have appealed against the ruling," Qarni said on Twitter.
Lacroix, of Sciences Po university in Paris, told AFP in December that changes late last year to the kingdom's highest religious authority confirmed an "anti-Sahwa, anti-Muslim Brotherhood" trend.
In 2010, Qarni was charged in absentia by an Egyptian court with funding the Muslim Brotherhood.
Agencies contributed to this report.