No it is not normal and there are a number of topics in the forums relating to always avast asking for reboot.
Operating system restart needed by avast message - First check the contents of the C:\Program Files\Alwil Software\Avast4\Setup\setup.log file (the last 50 or so lines), which should show you why it thinks the reboot is needed.
This could be solved, in some systems, by deleting the file C:\Program Files\Alwil Software\Avast4\Setup\reboot.txt
If that doesn’t resolve it check this:
You can also check this registry entry (right after computer restart):
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager, if it contains “PendingFileRenameOpertaions”.
Check its contents and if there’s only “reboot.txt” from avast4\setup folder, delete PendingFileRenameOperations, don’t delete any other key.
Back-up (export) the registry key before you edit/delete, just in case.
If none of the above are the cause it could be a tweaking issue that is having an effect on avast: