Eric Lemer, an author of popularmechanics.com has a solution for you.
One of the most spread features of cryptojacking is an immediate abrupt change in overall performance of the computer. Is might kick on or slow down your machine.
“If you notice either of these conditions and get suspicious, just pull up your Task Manager on Windows (Ctrl+Alt+Delete) or Activity Monitor on a Mac (Command + Space and search for “Activity Monitor”). If your web browser is pulling a particularly high percentage of CPU power (close to all of it), there might be a cryptojacker at play.
If you suspect a certain website is to blame, you can test your theory by closing the tab and monitoring the results or, in Google Chrome, go to the Menu, then More Tools, then Task Manager to check CPU usage by tab.”