Yes, if they are made of biodegradable compostable plastic. Compostable bags shall contain one of the following symbols:
Bags made of biodegradable plastic are "soggy" to the touch and are made from corn starch, potato starch or polyester. When looking at the bag, you should refer to the conformity marking of EN 13432:2002 and look for the phrase "Biodegradable product complying with EU legislation EN 13432" on the bag, which is usually displayed on the side or front. A second option is to look for the logos that attest to the certification of biodegradability such as "OK Compost" and "Compostable".