President Viktor Yanukovych asked the commission last week to consider whether Tymoshenko should be pardoned, Russian news agency RIA Novosti reported.
He forwarded a petition from 20 women in the Ukrainian Parliament asking for her release.
"Under the law, there are no grounds for the pardon," Deputy Prosecutor General Mikhail Gavrilyuk told RIA Novosti.
Tymoshenko served as prime minister in 2005 and again from 2007 to 2010. She was convicted in 2011 of exceeding her authority by signing a natural gas deal with Russia.
Tymoshenko, her supporters and critics of Yushchenko's government, including many EU leaders, say the prosecution was political. Tymoshenko heads the Party of Regions, which has its strongest support in Russian-speaking areas of Ukraine.