Did some African Americans during the Revolutionary War remain loyal to Great Britain and oppose the independence of the United States?

The brief answer to this is "yes, but not very
many."

There was one official regiment of African American
slaves who fought for the British.  They were organized in Virginia and were called Lord
Dunmore's Ethiopian Regiment.  Around 1100 slaves joined the regiment, with the promise
of being freed after the war.  It may, however, not be all that correct to say that they
"remained loyal" to Great Britian.  This is more of a case of them going with whichever
side seemed likely to free them.

We can see this from the
fact that a larger number fought for the Patriot side.  Somewhere close to 10,000 slaves
are believed to have fought in the Continental Army.  Most of these slaves were also
hoping to be freed after the war.

So, there were slaves
fighting on both sides, hoping to become free after the war.  Please follow the link
below for more on this.