Mahroug said she will hold a protest Thursday outside the court in Milan, the Italian news agency ANSA reported. She said her aim is "to protest not being heard during hearings."
Berlusconi allegedly had sex with Mahroug when she was under age, something she denies.
Mahroug was summoned as a witness in December but her lawyers said she was vacationing outside Italy. She appeared in January, but the court granted a defense motion to keep her off the witness stand, instead using statements she made to police.
The trial is currently suspended while a higher court considers a motion to move the proceedings away from Milan. Berlusconi's lawyers say the judges have a political agenda and are biased against their client.