We always recommend protecting surfaces not intended to be sealed as part of the preparation steps.  However, accidents happen and removal is easy with a cloth or sponge while the sealer is wet.  Typically, denatured alcohol, mineral spirits, or xylene will remove dried sealer.  Depending on the surface that is at issue, you may need to contact the manufacturer to ensure that any of our recommended removal products won’t have an adverse effect (e.g., paint manufacturer).  As always, we recommend testing the removal method on an inconspicuous area first.