Judge Norma Sandoval ruled on Thursday that Maria Corina Machado and three other members of her Sumate group - which helped organise a referendum against Venezuelan President Hugo Chavez nearly a year ago - are being charged with "conspiracy to change Venezuela's republican system".
The accused say Chavez's government has trumped up the charges against them in an attempt to intimidate critics who say his rule is becoming increasingly authoritarian.
Chavez has called Machado a traitor after her Sumate group received funding from the US Congress.
The president won the August recall referendum organised by Sumate, which said the vote was plagued by irregularities and held under conditions that favoured the president.
The judge ruled that Machado, Alejandro Plaz, Luis Enrique Palacios and Ricardo Estevez should be tried in court but did not set a date. She said they could remain at liberty until the trial took place.
Despite winning a referendum,
Chavez has many detractors
"For us in Sumate, it's very clear this persecution is intended to intimidate us," Machado said.
One of Venezuela's best-known opposition figures, Machado met Bush at the White House on 31 May. The heavily publicised meeting further strained already tense ties between Venezuela and its biggest energy client, the United States.
US officials praise Machado as a pro-democracy campaigner. She is the only Venezuelan political figure whom Bush as formally received.
Venezuela's government said the meeting showed Sumate was an "agency" of the Bush administration, which Chavez accuses of plotting to topple or kill him.
Sumate says it received a $31,000 grant from the National Endowment for Democracy, a US group that is allocated funds by the US Congress to promote democracy worldwide.
Sumate leaders say they used the funds to organise courses for voters about their electoral rights.
Chavez says the National Endowment for Democracy is a front for the CIA, spearheading US efforts to end his rule over the world's fifth largest oil exporter.
The US government and leaders of the National Endowment for Democracy deny his accusation.
Machado and Plaz said on Thursday they would continue to campaign for transparency in upcoming local parish elections scheduled for early next month.