Absolutely!!! I take Rex out all the time in the winter to play in the snow! Just make sure it's not really wet, because that's bad for buns. When I take Rex out I try to keep it to 10 minute periods and we don't go out at all if it's less than 15 degrees out.
If you do take your bun outside, watch out for "chapped" ears. If the ears or nose area seem to be flaky, dry, or inflamed stop taking your bun out, it's sort of like getting chapped lips from the cold, dry air outside. Rex got flaky ears once , a vet can usually give your bun something to help with it.