The government has this month put the old Royal Australian Mint Administration building in Deakin on the market, four years after it announced the block would be sold off.

The Denison Street building is leased to Questacon's Ian Potter Foundation Technology Learning Centre, which runs science and technology workshops for school children.

The government department which administers Questacon's programs had insisted the centre would not be forced out, with terms of the sale agreement guaranteeing it at least another 10 years.

But Labor MP for Bean David Smith had reservations about the sale, writing to Prime Minister Scott Morrison to urge him to reconsider it.

In the letter, Mr Smith said the sale terms meant there would be uncertainty beyond the initial 10-year lease period.

Mr Smith raised concerns about the "potential escalation of costs" for the tenant, with the private buyer guaranteed 3.5 per cent annual rent increases under the terms of the sale. Gross annual rents started at more than $900,000.

"The building itself is iconic and particularly fit for this purpose," Mr Smith said in the letter seen by The Canberra Times.

"It would be a pity for such a building to move from public to private hands and is another example of a critical national institution having key functions based in leased land."

Mr Smith said Questacon had made good use of its government funding in the past 30 years, but it would need ongoing support with staffing and infrastructure to "take the next step" in the coming decades.

"The Australian government has made positive noises about the importance of science and engineering education but needs to back this up by long term investments in organisations such as Questacon and the Ian Potter Foundation Technology Learning Centre," the letter read.

"I urge you to rethink this decision."

Questacon director Graham Durant said the sale had been expected as part of the federal government's divestment policy and operations would not be affected.

"We will be continuing to build exhibits and run technology learning programs in the building as before," Mr Durant said.

The government agreed to the divestment of the Mint Administration Building in the 2016-2017 budget.

An application to the National Capital Authority to rezone the location to allow for a health centre and consulting suites, to fit in with the health facilities already in the area, was approved in 2018.

This rezoning followed an extensive refurbishment ahead of the science centre's move in 2012. The fit-out involved removing almost all original partition walls.

National trust spokesman Eric Martin said provided the heritage values were conserved, which included the exterior and some internal details, the actual ownership was not that critical.

"The use is also a consideration as it has always been a public building so a public use is preferred," Mr Martin said.

Mr Martin said the broader issue with the sale of the learning centre was the future of the area around State Circle in general.

"And the setting of the mint, which also needs to be considered," Mr Martin said.

Questacon founder Mike Gore said he did not believe the future of the science centre or its employees were at risk.

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A spokesperson for the government said Questacon was, in fact, expanding the number of staff based at the site as part of a $14.9 million package to design cyber and engineering challenges for teachers and students.

Professor Gore established Questacon at the old Ainslie Public School after visiting San Francisco's Exploratorium.

It was moved to the Parliamentary Triangle in 1988 and the Ian Potter Foundation Technology Learning Centre opened at Deakin in 2012.

The property would be marketed for sale through an open market tender, which closes on March 24.

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