Wilders, who has courted controversy with his hardline anti-Islam, anti-immigrant stance and his incendiary insults against Moroccans and Turks, has long been under 24-hour police protection.
But tensions are escalating ahead of the March 15 election in which the MP's Freedom Party is running neck-and-neck with the Liberals of Prime Minister Mark Rutte.
On Saturday, Wilders upped the tone at the launch of his official campaign, denouncing "a lot of Moroccan scum who make the streets unsafe".
National police spokesman Dennis Janus confirmed to AFP that an agent had been arrested on Monday suspected of "violating official secrets".
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"The police together with the public prosecution service are currently investigating," Janus said, but declined to give further information.
Citing high-level police sources, the NRC daily reported that an agent had handed over information about Wilders' movements to a Moroccan-Dutch criminal organisation.
The leak was serious enough to trigger talks between Wilders and his political foe Rutte, who also refused to comment to reporters afterwards.
It was not immediately clear whether the agent was directly involved in Wilders' personal protection.
But Wilders, who was last year convicted by a Dutch court of discrimination, said in a tweet: "If I cannot blindly trust the (team) that has to protect me I can't function. It's unacceptable!"
Dutch police chief Erik Akkerboom told news radio station BNR: "What we know up to now, is that (Wilders') safety was not in question.