A baby teething at 6 weeks old is rare but a 6 week old baby can be teething.
Babies can also begin teething at 2 months of age although the full teeth don't start coming through until the baby is 6 months of age.
All babies are different and I've seen a baby before start teething at 6 and 7 weeks of age so it's certainly possible for the baby to be teething at 6 weeks old.