Yes, with some simple precautions, you are reasonably safe.
- Do not browse porn or humor sites with flash enabled or without an adblocker.
- Do not open unsolicited e-mail attachments. Especially, don't treat the sender address as authentication - look for text that positively identifies that it's the real sender and why it was sent.
- If you get a suspicious pop-up, don't click its close button, because it could be a visual overlay for the "install" action. Use ALT-F4 to close the browser.
- If in Windows, go to Folder Options - View, and uncheck "Hide extensions for known file types". Then you will see that the attachment that looks like funnycat.jpg really is funnycat.jpg.exe
Thing is, even with antivirus installed, most new infections will go straight past the AV and infect your PC. The reason is of course that those who write malware test it against the AV software first, and make changes until it passes. Then they have several days until the AV software recognizes the change, and they make another permutation. The net effect is that the AV software will scan enormous and ever-growing lists of signatures, and slow your system down more and more, while all new malware still gets through.
An observant user, on the other hand, stops most new malware. Unless you're specifically targeted by a hacker, you're reasonably safe.