The decision will not disrupt government operations, the Infocomm Development Authority (IDA) said after local daily The Straits Times reported that some 100,000 computers would be affected.
"We have started to separate Internet access from the work stations of a selected group of public service officers, and will do so for the rest of the public service officers progressively over a one-year period," the IDA said in a written reply to AFP queries.
Singapore is one of the world's most Internet-savvy societies, offering broadband speeds envied by many.
A wide range of government services are available online, including registering for marriage, filing complaints to the police and video consultations with doctors.
Also Read
Government services will not be disrupted by the security measures, sources familiar with the plan said.
The Straits Times said public servants would still have access to the Internet on their personal devices such as tablets and smartphones.
The IDA said the government regularly reviews measures to make its network more secure.
"There are alternatives for Internet access and the work that officers need to do, does not change."
Singapore announced in 2014 it was stepping up IT security measures following attacks on a section of the prime minister's website, as well the website of the presidential residence.