Senator Kelly Loeffler is in isolation after both positive and inconclusive virus test results.

Senator Kelly Loeffler of Georgia, a Republican who is campaigning in a high-stakes runoff election that could determine control of the Senate, is isolating after receiving both a negative and positive test for the coronavirus on Friday and then receiving an inconclusive result on Saturday, a campaign spokesman said.

Ms. Loeffler has worn masks while interacting with people, but was indoors and unmasked among unmasked crowds at an event on Thursday. She wore a mask while greeting voters who lined up to meet her.

On Friday morning, she took two coronavirus tests, according to her campaign spokesman, Stephen Lawson.

One of those was a rapid test, which came back negative, and Ms. Loeffler “was cleared to attend” events on Friday, including a rally with Vice President Mike Pence and Senator David Perdue of Georgia, Mr. Lawson said. But the second test, a polymerase chain reaction, or P.C.R., test — which is considered more accurate — came back with a positive result after her events on Friday evening, he said.

Ms. Loeffler, 49, was tested once again on Saturday morning and received an “inconclusive” result on Saturday evening, Mr. Lawson said.

The senator followed C.D.C. guidelines by notifying those with whom she had had sustained contact while she awaits further test results, he said.

Ms. Loeffler has held recent events with prominent Republicans, including Mr. Pence, Senator Tom Cotton of Arkansas and Mr. Perdue, who is also engaged in a runoff election that could determine control of the Senate.

“She has no symptoms and she will continue to follow C.D.C. guidelines by quarantining until retesting is conclusive and an update will be provided at that time,” Mr. Lawson said in a statement.

A spokesman for Mr. Pence, Devin O’Malley, said that “as he awaits a confirmatory test from Senator Loeffler, Vice President Pence is in regular consultation with the White House Medical Unit and will be following C.D.C. guidelines as he has in other circumstances when he has been a close contact.”

The last time Mr. Pence was deemed a close contact was last month, when his chief of staff, Marc Short, tested positive.

Mr. Pence continued to campaign then, with the White House saying that he was performing “essential” duties that exempted him from Centers for Disease Control and Prevention guidelines calling for people to quarantine for 14 days after exposure to the virus.

Ms. Loeffler, a businesswoman who is the Senate’s richest member, was temporarily appointed to her Senate seat late last year. She faces the Rev. Dr. Raphael G. Warnock, a Democrat, in an election on Jan. 5, when Georgia voters will also decide between Mr. Perdue and his opponent, Jon Ossoff, a Democrat.

Astead W. Herndon contributed reporting.