Depends on what you mean by active objects..
Are they moving, do they have transparacy, are there events performed on them every tick, How big are the images, how many collision-points do they have, are they instances of the same object or different objects alltogether?
This topic might help with optimizing:
https://www.scirra.com/tutorials/298/pe ... bile-games
But there are many more tips and tricks scattered over the forum and tutorial-section.