Yes it is, especially on new (and potentially hostile) ground. You can help by covering the run by beach towels, so piggies feel more protected. Dot little hideys around (about 1 foot apart), so they have safe places to explore from. The hideys can be as simple as cardboard boxes with a door opening. It will usually take a few daya and a few trips to the lawn until new guinea pigs are confindent with new surroundings.
Talk to them as often a you can, sit still next to the cage/hutch or run and lure them with little treats. Don't hover over them like a predator. get them used to your hands around, but in a way that they associate them with nice things.