What everyone else has said.
Also, though, if you do acquire an infection while in Safe Mode, it may not be able to run services it needs to do its thing. So you may not end up effectively infected until you reboot in Normal Mode. That will vary from virus to virus, though.
If you think you've picked something up, and you can do it, it would be best to run an antivirus sweep in Safe Mode, with a current antivirus proggie, before restarting in Normal Mode.