El-Beblawi said Mubarak would remain under house arrest at the Maadi military hospital despite an August court order to release him, Ahram Online said Thursday.
El-Beblawi told al-Masry al-Youm Mubarak would be transferred to temporary detention in accord with criminal procedures despite the end of emergency law by the middle of the month.
Some experts, however, have raised doubts about the legality of el-Beblawi's decision, Ahram Online said.
Egyptian lawyer Shawky el-Siyad told the website Mubarak should be released once the state of emergency ends, saying there are no legal grounds to keep him under house arrest.
"This is not within the prime minister's powers. Only a judge can send Mubarak to temporary detention. If el-Beblawi does this it would be interfering with judicial authority, and totally unacceptable," el-Siyad said.
Mubarak is facing retrial for the deaths of protesters during the January 2011 uprising that led to his ouster, as well as corruption.