There are reports of people dressed as clowns deliberately scaring other people.
A number of police forces have been getting calls from those who've been frightened.
Newsround has been looking into what's happened.
These school children have been telling Newsround what rumours they've heard about clowns and how they feel about it....
It started in the US
This is something that started in the USA and then spread to other countries, like Canada and Australia.
There have been loads of rumours going round, and it's quickly spread online with people posting videos and photos on social media.
Police are taking it seriously
The police say there's nothing funny about it.
"It's not a joke now, so stop it" is the warning from Northumbria Police official Vera Baird.
She added that there were going to be extra patrols around the areas where there have been problems.
Police forces around the country say they will deal with people whose behaviour might harm others.
It could be a crime
Police are also warning that scaring people like this could be a crime.
Merseyside Police said: "Doing this to a stranger may cause alarm or distress and could constitute a criminal offence such as harassment."
One man in Gwent, south-east Wales, has been given a criminal record for deliberately frightening people.
Social media threats have not happened
False rumours can spread really easily on social media. People can believe or share things that aren't true.
One social media account, which has now been taken down, was claiming that clowns would turn up at schools in the Liverpool area.
But Merseyside Police has said that no people dressed as clowns have turned up at any schools.
There have also been no reports of anyone being hurt.
If you're worried
Remember that events are in the news because they are rare.
If you're worried about it, then it's important you talk to someone you trust, like a parent or a teacher.
There's more advice here on what to do if you're upset by the news.