The man and woman in their 30s and and woman in her 50s returned positive test results while in hotel quarantine.

"They have been in a medi-hotel since their arrival and there is no public health risk," the SA health department said on Saturday.

One of the cases is an old infection and not active, the department said.

There are six active cases in the state in total.

Meanwhile, the SA government is concerned about clusters in NSW but has not yet re-imposed border restrictions on that state.

Premier Steven Marshall has said five clusters are of concern to SA but particularly the one centred on Bargo, 100km southwest of Sydney.

On Saturday seven new cases were reported there - five locally acquired.

"We are increasingly concerned about clusters in NSW," Mr Marshall said on Friday.

"I don't think there is a decision (on borders or other measures) which is imminent.

"But our focus since day one has been to listen to the expert advice, act quickly and keep the people of South Australia safe."

The state has recorded 482 cases in total since the pandemic began and four deaths. About half a million South Australians have been tested.

Australian Associated Press