Yes, it is safe to ride in the rain. Just take it easy and avoid the following:

-- painted lines and other painted markings on the road - they are slippery
-- railway tracks - they are really slippery
-- leaves and muddy areas - they can be slippery
-- puddles - you never know what size hole a puddle might be hiding

Then clean your bicycle when you get in. Wipe it down. Clean off any mud.