I've windows 7 installed on my PC & the antivirus software is expired. Is there any best virus removal program for free.

There are various virus removal software available in free version but no surety that you pc always would be clean and virus free

would you suggest any ?

just download malwarebytes and run in safe mode.

This is free, no drag on system resources and it works: Microsoft Security Essentials http://www.microsoft.com/security_essentials/?mkt=en-us change your location\market if needed.

Sorry, forgot to mention, uninstall the trial version that's currently on the computer first before installing another security program. Here are the vendors partnering with Microsoft for your own research: http://www.microsoft.com/windows/antivirus-partners/windows-7.aspx

Thanks Nano, I will give a try.