Police in Philadelphia are investigating an alleged plot to attack the Pennsylvania Convention Centre where election ballots are being counted.
They received a tip that either an individual or a group was travelling to the city from Virginia in a Hummer with the intention of attacking the convention hall.
A man has been taken into custody and a weapon recovered.
It is not known what charges the detained individual is facing.
The group that the police were tipped off about may be a family, according to reports.
The eyes of the nation are on Pennsylvania as workers continue to tally hundreds of thousands of mail-in ballots that could decide who sits in the Oval Office for the next four years.
In Philadelphia 95 per cent of votes have been counted. Donald Trump has 49.5 per cent of the vote, while Joe Biden has 49.2 per cent
Tallying the votes is happening against a backdrop of legal challenges and inflammatory rhetoric by Mr Trump who has baselessly claimed that there is widespread voter fraud.
The Trump campaign tried to stop the count in Philadelphia, alleging that city officials were not giving access to Republican count observers. A federal judge urged both sides to come to an agreement.
At a press conference on Thursday, Mr Trump accused Democrats of trying to steal the election. There is no evidence that is the case.
With tensions high and protests and counter protests occurring outside ballot counts, there are worries that conspiracy theories and other allegations may lead to violence.