It "could" be normal.
One of the "downsides" of 4 stroke outboards is that they'll sometimes "make oil"--so to speak. In other words, the oil level can rise. This is most common on motors that are used in cold climates and cold water and/or do a lot of idling/low speed running. If this describes your type usage, it is considered mostly normal.
So what happens is that a small amount of fuel and air get past the piston rings and into the crankcase. Over time it builds up, UNLESS the engine is run enough, and hard enough, to get the engine oil above about 150 degrees F, at which time the contaminants will boil off.
How to prevent. Change oil more frequently if you do a lot of idling and/or run often in cold temps. Or just make a few laps around the lake at half throttle or more which'll boil off any unburned hydrocarbons and any moisture.
Also-if a thermostat sticks "open", they'll do the same thing. And-it's hard on the engine. The thermostat needs to work and work properly especially on an EFI engine that is dependent on engine temp to calculate the fuel injection.
Not to say there ain't a problem...but a little is normal, happens over time. But if it's excessive and happens in a short amount of time, you may have another issue-such as a leaky fuel pump, or whatever.