Office 365 personal includes virus protection and other types of protection like anti phishing, anti spam protection, link and attachment scanning for email and also for files stored in onedrive.
You can see more info about the Office 365 protection it includes here
It is important to note though that this will protect your emails in outlook and any files saved in onedrive but not provide any protection to any other files on your computer so if you are using norton 360 to protect your PC then you should continue to do so or ensure that you use an alternative anti virus product should you choose to cancel.