The only difference with using a keyboard is that the keys may not be weighted (be louder/softer depending on how hard you press), there may not be any pedals (used to change the sound of music, although not important for beginners) and there may be less octaves on your keyboard (each octave is 8 notes wide, for example, from one C to the next closest C). As you appear to only be starting out, however, none of these factors should present you with a problem. As you advance, you may need weighted keys, pedals or a bigger keyboard, but you can get around this by learning as much of the song possible on your keyboard and learning the parts your keyboard won't allow for during your next lesson.