Installed a new high efficiency furnance/air handler in the attic this past summer and seeing that the unit drips water even during the winter months with only heat on - is this correct? If OK, will need to reroute drip pipe to inside wall as line is freezing up in this cold weather.

Yes a high efficiency furnace produces condensate so it will have liquid draining out of the unit durning the winter. Where you run the pipe to protect it from driping is up to you but follow the manufactures or local code directions as to where the liquid is supposed to go in the end.