Ruling Socialist Party leaders in May accused a group of opposition activists including Machado of planning Maduro's assassination to pave the way for a coup. Opposition critics dismissed the accusation as a charade based on forged documents.
Machado, a former legislator and high-profile adversary of the government, helped spearhead three months of protests earlier this year. She will be formally charged on Dec. 3, the prosecutor's office said in a statement.
Via her Twitter account, Machado suggested the announcement was in retribution for demanding new leadership at the state elections council. A representative for Machado said she was not immediately available for further comment.
In May, prosecutors called her in to testify as a witness in the case. At the time, she dismissed the Socialist Party's accusations as "infamy."
The Socialist Party has frequently made high-profile accusations about opponents without providing strong evidence. Adversaries dismiss such campaigns as political stunts.
Government supporters point out that the opposition in 2002 staged a brief coup against late President Hugo Chavez and launched several national strikes as part of failed efforts to force him from office.