The man, 25, is accused of being behind a post that predicted January 7 — the anniversary of the toppling of the Khmer Rouge by Vietnamese-backed troops — would bring Hun Sen’s death.
“He was arrested yesterday (on Thursday). He was sent to Phnom Penh municipal court this morning,” Am Sam Ath, an activist at local rights group Licadho, told AFP.
He faces up to two-and-a-half years in jail if found guilty on charges of issuing the apparent death threat as well as insulting the premier.
The arrest was made a few days after Hun Sen launched a new mobile app and a website in an attempt to engage the public, especially young voters, many of whom support the opposition, which made major gains in 2013 elections.
While Hun Sen has said he was open to constructive criticism, he has warned Facebook users who insult him that they could be easily traced.
Last year, a 25-year-old student was arrested over an alleged Facebook post calling for a “colour revolution” in the country.
A Cambodian opposition senator was also held for posting a doctored document on Facebook about the border with Vietnam, a deeply sensitive issue amongst nationalists in Cambodia.
He faces up to 17 years in jail if convicted.
Cambodia opposition leader Sam Rainsy has been linked to the same offence and is currently in self-imposed exile to avoid arrest warrants associated with that incident and an old defamation case.
Hun Sen, one of the world’s longest-ruling leaders, marked three decades in power in January. He is regularly criticised by campaigners for stamping out dissent.