Belarus' public prosecutor's office requested 12 years in prison for Maria Kolesnikova, one of the main leaders of the opposition movement.
She is accused of wanting to overthrow the authoritarian regime of President Alexander Lukashenko.
The trial of 39-year-old Kolesnikova, which began in early August, comes after months of crackdowns in Belarus.
Thousands of opponents of the regime have been arrested or forced into exile since the disputed election of Lukashenko last year.
Kolesnikova has been imprisoned for 11 months and is on trial alongside her former lawyer Maxime Znak.
"Kolesnikova and Znak face up to 12 years in prison. The closed-door deliberations took place today and the prosecutor requested this sentence," the press service of Viktor Babaryko said in a statement.
The defendants worked for opposition politician Babaryko who was sentenced to 14 years in prison in July.
Kolesnikova was arrested in September after resisting an attempt by authorities to expel her from the country by jumping out of a car window and tearing up her passport.
The verdict is expected to be delivered on September 6.