The ruling comes as Horst Koehler, the German president, considers a pardon for Mohnhaupt's former RAF colleague Christian Klar, who has also spent the past 24 years in prison.
Mohnhaupt, 57, was arrested in 1982 and sentenced to five life sentences for her role in the murders of leading German figures including industrialist Hanns-Martin Schleyer, Dresdner Bank head Juergen Ponto and federal prosecutor Siegfried Buback.
Also known as the "Baader-Meinhof Gang" after founders Andreas Baader and Ulrike Meinhof, the RAF rose from the student protests of the late 1960s and the anti-Vietnam war movement.
Its members started by experimenting in alternative lifestyles in the communes of West Berlin and Hamburg before turning violent in a campaign of assassinations, kidnappings and bombings against the German elite and US military personnel.
The group, which announced that it was disbanding in 1998, is suspected of killing 34 people between 1972 and 1991. About
26 RAF members died during that period and another 26 were sentenced to life in prison.
Many of them, mostly secondary members, have since been released or pardoned and now work as teachers, accountants, filmmakers and journalists, some under assumed names. Only four, including Mohnhaupt and Klar, remain imprisoned.
Mohnhaupt was a prominent member of a second generation of RAF members who continued the class war after Baader and Meinhof were caught and committed suicide.