Meles Zenawi: Ethiopian leader
Meles Zenawi has led Ethiopia for more than 20 years
However, Bereket Simon declined to give any details about Mr Meles' whereabouts or what he is suffering from.
Mr Bereket had earlier been quoted as saying the prime minister, 57, was on holiday.
Speculation began when he missed last month's African Union summit.
There were reports that Mr Meles was in hospital in Belgium, suffering from a stomach complaint.
But Mr Bereket was quoted as saying by The Reporter newspaper that opposition forces were trying to "create confusion" by talking about the prime minister's health.
He told the BBC Focus on Africa programme it was "not useful" to provide more details.
When asked who was in charge while Mr Meles was being treated, he replied: "The status quo is maintained - there is no change and there will be no change in the near future."
It is believed that Mr Meles' last public appearance was at the G20 talks in Mexico in June.
He took power as the leader of a rebel movement which ousted the communist government of Mengistu Haile Mariam in 1991.
He has won several elections since then, but his political opponents have accused him of using repression to retain power.
Source: BBC News