The law protecting the monarchy was passed in February. Critics say it further erodes freedom of speech and political activities, already under stress from Prime Minister Hun Sen's government.
Police said Khieng Navy was arrested in his home yesterday and could face five years in prison if convicted.
He is accused of posting comments online that allegedly insulted King Norodom Sihamoni by suggesting he was behind the November court decision to disband the main opposition party to benefit Cambodia's enemies.
Sihamoni is a constitutional monarch with a minimal role in public affairs, while Hun Sen exercises almost absolute control over politics.
Offenders of the law on lese majeste, or insulting the monarch, could be punished by one to five years in prison and a fine of up to 10 million riels (USD 2,500).
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