Not to be too picky, you've got 4 cores, capable of running 2 threads each. Where do you see (in what program) that thread #6 is running constantly? Please provide a screenshot.
Open Task Manager. Click on the Processes tab. Click on the "Show processes from all users" button. Now click on the CPU column so it sorts from highest to lowest based on CPU usage (if it sorts from lowest to highest, click on it again). What is showing up at the top of the list? Please provide a screenshot.