Salem, who is accused of having amassed billions from his close association with the former president, had fled to Spain after a mass uprising broke out in Egypt, toppling Mubarak.
In March last year, he was sentenced to 15 years for involvement in corruption in a land deal. In June, however, he was acquitted, along with Mubarak, of corruption charges in Egypt's natural gas export deal with Israel.
A Spanish court, however, had ruled against his extradition to Egypt.
Salem's lawyer Tarek Abdel Aziz said that he has met Mostafa Al-Husseiny, attorney general at the Public Funds Prosecution, and proposed a reconciliation agreement whereby Salem would return half of his properties.
Abdel Aziz said in an interview with CBC satellite channel that Salem would also disclose all properties and assets inside and outside Egypt.
Salem proposed a reconciliation agreement six months ago, according to Abdel Aziz, despite a ruling by the Spanish Supreme Court saying he could not be extradited to Egypt.
In December, Spain's Constitutional Court ruled against an earlier decision to allow Salem's extradition to Egypt after accepting his appeal.
Egyptian authorities have recently begun to accept reconciliation agreements with former officials, lifting charges in return for recovering stolen assets.
Earlier this month, the Public Funds Prosecution agreed to drop charges against former prime minister Ahmed Nazif in exchange for him repaying funds he illegally received in the form of gifts allegedly from the state-run Al-Ahram newspaper.
The Public Funds Prosecution said it has retrieved around LE 1 billion of illegally acquired money from former officials.
