It might be helpful if you post a little more info...what type of fridge, perhaps what RV it's in, etc....
then someone with knowledge or experience will chime in with better info.
That says, odds are you don't have a frost free fridge. Also the more the door is opened over time the more humidity can enter. my RV fridge does not ice up over a typical weekend, but I did have a noticeable amount at the end of our 19 day trip last summer... a typical electric/gas RV fridge
Yes, in general terms anyway. Moist air is getting into the fridge and the water condenses on the coldest parts. The most common explanation is that people keep the door open too long (or too open it too often) on warm humid days. The other explanation is that the seals around the door are leak and letting air in at a slow buy steady pace. The "dollar bill test" is an easy check for that. Using a fresh and reasonable crisp $1 bill, close it between the door and the frame and pull it out slowly. You should feel modest resistance if the seals are tight. Repeat the test all around the doors to find spots where there are gaps.
If you are talking about an RV type Propane/Electric Absorpition cooling unit. Nothing at all. 100% normal, Nothing to worry about. Just defrost as needed. I'd be more worried if it did NOT happen though there are things you can do to reduce it. More on that in a paragraph or two..
If you are talking about say a 1965 Residential Fridge..where the "Freeezer" is a compartment inside the refrigerator at the top.. SEE above.
IF you are talking about a modren Residential/office/dorm/Bar frostfree. Problem
I reduced the frosting on mine by adding a couple of computer fans. one is "Bigger" (air flow wise) and keeps half the fins almost frost free.. The other ther eis some build up
For about 100 dollars give or take a bit you can get a fan/led light thing that attaches to the top of the fridge compartment. This is supposed to do an even better job of reducing frost in the FRIDGE.
Freezer.. alas it does not help. I really need to do a freezer defrost soon myself.. To do this I'll freeze some ice substitute bags I get every few months (about time to place another order for those too) and move them to the nearly frost free due to fans fridge.. Then the little frozen food I have will go in the #2 Freezer or aux storage (with ice blocks) while I shut it down and open the Freezer door.. Lots of fun sucking the water out.. I think I have a "Trick" for that though (lots of frost - lots of water and unlike the fridge.. NO DRAIN. so I need to use a sucker. I just figured out I have one 12 volt too)
I have a Dometic RV fridge and had problems with the fins, below the freezer in the refrigerator section, icing up on long trips. I also had a lessor problem with freezer ice buildup. I checked my seals in the doors and all was fine. I installed the "Fridge-fix" from "Smart RV Products". It installs with Velcro under the freezer and blows air through the fins. Mine is the 3 fan model. That completely solved the ice problem on the fins in the refrigerator section as well as keeps the refrigerator section much cooler!! We now never have any ice on the fins. Mine was an easy install...Just pull the plastic off the Velcro and stick the unit in place. Then slip a ground wire clip on a fin and hook the power wire to the door switch, making sure to hook into the wire that stays hot when you close the fridge door. For the frost freezer we just got use to getting in and out of the freezer quicker to minimize the ice buildup. You can buy cheaper fan units for RV fridges but this one works far better than others I have seen.