If the external drive is running at the time, probably not a good plan to move the drive.
If the drive is disconnected (not running), and you don't accidentally drop the drive, then there shouldn't be any problem with moving wherever you like.
An older drive may need to have the heads 'parked', but any modern drive (like less than 15 years old) isn't under that limitation, and would set itself to the 'parked', or safe position by default at power down.