In the US, musicians refer to it as an "electric keyboard." If they're introducing the musician who plays it, they might say, "...and on electric keyboard is..." half the time, they might even shorten it to just, "...on keyboard tonight is..."
I wouldn't say either adjective is incorrect. Just different ways to express it, depending on the country, maybe.
"Electronic Keyboard" really does encompass the whole range of different types of keyboards, that would include synthesizers and such. You couldn't go wrong by saying that.
In casual speech, though, I would say either of your words would work.