This issue seems to occur when upgrading from a previous version of OS X rather than performing a clean install of Mavericks. This problem does not occur in the new 1Password 4 for Mac, but if you are sticking with 1Password 3 for some reason, we have a relatively easy fix for you. To resolve the problem, please follow these steps.
Copy and paste the following path into the input box and then press Return:
Move any and all
1Password.safariextz files you see there to the Trash.
Copy and paste this other path into the input box and press Return:
safari-extension_com.agilebits.onepassword-safari-2bua8c4s2c_0 that you see there to the Trash.
You will need to reinstall the 1Password extension in Safari after performing those steps, but everything should start working well once you do.