I wouldn't say it's "normal" to have big puddles of saliva..but it COULD be. He most likely IS teething..have you noticed him chewing on things a lot more? Is he eating okay?
Some things to keep in mind:
Toys that can be wetted and frozen can minimize any gum irritation. Soft chewies are better than hard ones.
Are there only certain times this is happening? Could it be stress as well? Is he showing any signs (other than hypersalivation) that may be caused by separation anxiety? Any changes in routine in the house?
Is he coughing? Swallowing hard? It could be his throat.
More details of WHEN this is happening may help..but if you think he's in discomfort, please speak to your vet.