I've recently noticed CPU spikes during start up and randomly throughout the day. I'm concerned because I can't find a cause. Task Manager doesn't register any apps or services using that much CPU. I've done multiple malware checks with no hits.
there are many reasons, if your connected to the internet it might be windows update checking the database. unless your having performance issues then in all likelihood normal.
It could be your antivirus software. I have Avast and sometimes I notice that my cpu usage shoots up for about 5-10 minutes and I figured out what it was. Unless it cripples your machine I would worry about it.