@Saravanakumar If it’s happening when you first turn on your laptop and isn’t just happening when you’re opening Brave, then it suggests you have adware (a type of malware) on your device. This is especially true if it’s a “random” website and it isn’t the same one. If it’s the same site each time, might be part of something you’ve installed.
In any case, I’d try to get Malwarebytes which I believe will let you have a free trial to scan and see if it picks up issues. At the same time, you may want to try to think back to anything you might have downloaded/installed for the couple months since you’ve been having issues.