They are aphids ... a very common pest on roses. They have piercing mouth parts, which they use to suck the plants juices. (They're harmless to you.)
I just wash them off with a stream of water from my garden hose. If there aren't too many, I just wipe them away with my fingers. Although they're a bit unsightly, they really don't do much harm to a mature plant, unless they are present in huge
numbers. Ladybugs are their natural predators, so if you see ladybugs on your roses, you probably don't need to do anything.
Another treatment is to spray with a solution of soap and water. I reserve this for extremely bad infestations. Be sure to use soap
, not detergent. Most dishwashing liquids are detergents. Carefully read the label on whatever you decide to use, just to be sure.