Yup, looks like orf.
It can get quite sore and sometimes puts them off eating. So it's worth washing it (Daz is the best thing to use, I kid you not) and putting some purple spray afterwards on to stave off further secondary infection. Also make sure they have soft grass available to eat, and maybe some pellets that won't stick to the sores. They may have sores inside the mouth which make it uncomfortable to chew, so perhaps also a feed block they can lick.
Remember it's highly contagious, to you and by you, so wear gloves and change your clothes after handling them or being in their pen.