Normal? Sure. Can be caused by over-pitching your yeast, using a more active yeast or richer wort than normal, or over-filling your fermenter. You'll need to do something quick before your fermenter blows its lid off (risking infection of the beer and making a gawd-awful helluva mess).
The easiest solution is to always start your ferments (for the first 1-3 days) with a blowoff tube. For 5-gallon batches in buckets, the easiest way is to sanitize a length of 3/8" tube (use the one from your siphon or bottling wand). Just pull out the airlock and shove the end of the hose into the grommet hole. (If you have a 3-piece airlock, a 3/8" ID hose can also slide onto the vertical shaft inside, although you'll want to clean and sterilize it anyway.) Be sure to put the other end of the hose into a bucket or bottle of sanitizer solution (use the same mix you used to sanitize the hose). This will prevent airborne critters to migrate back up the hose into your fermenter (basically a long airlock with room to bubble crap through). Place the bucket/bottle/jug (I use gallon water jugs) at the same level as the bottom of your fermenter or lower, and prop the hose so that liquid can't pool in a bend. After a couple of days, the ferment will slow and you can switch back to an airlock.
If you primary ferment in a glass carboy or better bottle, there are 1" OD hoses available from homebrew suppliers in 3' lengths that you can just shove into the neck and not worry about a bung or cap.