My 3 year old Maltese bison, is normally a calm dog. she eats, play and is well. regularly during the day,?

It could be, dogs of any breed can have seisures or it might be that she/he might have a disease. It might also be anxious about something. When did the shaking start? Did any thing happen before the shaking started? In any case try taking it to a local vet to see whats going on.