It's important to acknowledge that mystery is an essential element in every genre. If there are no secrets to uncover, why bother? If there aren't questions raised, why turn the page and read on? Whether you write romance, suspense, sci-fi, historical, or something else, your story must have an element of mystery.
At its simplest, a mystery is a puzzle. A crime has occurred (often offstage), and the protagonist must uncover the truth. Mysteries are intellectual games of whodunit. Clever plotting, fair clues, detective reasoning skills--all of these are important when a mystery novelist constructs the story.
A suspense novelist works with a threat and imminent danger that must be resolved rather than just a puzzle to be solved. Something is coming. Do you hear footsteps? Thunder? Breathing? The ticking bomb concept is very much a part of the suspense novelist's arsenal. A suspense novelist builds an emotional roller coaster and makes sure it collapses at the right time--with a bang.
The suspense protagonist is thrust into the role of Hero, often without preparation or skill. He or she would rather be safe at home, but something or someone has made it impossible for that to happen--usually putting the Hero's home and loved ones in mortal peril. The stakes are much higher in suspense; the intensity and threat upped to an almost impossible level.
And finally, a successful ending for a mystery is intellectually satisfying, while a successful ending for a suspense novel is emotionally satisfying.