Sure you can! Some antivirus providers even provide firewall with them. If you want a stand-alone firewall, then I recommend going for COMODO Personal Firewall.
Antivirus software is very important. Everywhere throughout the Internet, there are viruses, malware, spyware, adware and other very harmful things, and a good antivirus acts as a wall against these....
There can be a lot of reasons why. Your software (definition files) might not be up to date. Also, its possible that the company your using does not have the malicious software in their "banned" list...
I do not recommend this event, two antivirus not only improve your computer protection, but also decline your computer speed. Even though I have done it by my self. Though I picked the right...