While BB guns don’t typically produce enough noise to warrant the use of a suppressor, there are indeed suppressors available for them. Whether or not you need one is another question entirely. Whether shooting indoors or out, always use eye and ear protection. Sound suppressors help reduce the muzzle blast of a shooting firearm, making it more pleasant for the shooter and those nearby. They also can help reduce continued exposure to loud noise, which can cause permanent hearing damage. Muffs and plugs are great, but only if they’re used consistently.
A quality sound suppressor can be a valuable addition to any airgun, especially if mostly shooting in populated areas. The report of most rimfire caliber rifles is significantly reduced when using a good quality sound suppressor. For pellet guns, high-velocity models such as the Crosman Benjamin Marauder or Gamo Whisper can also be fitted with a sound suppressor to help reduce the muzzle blast.
Do note that while most states allow private ownership of suppressors, there are a few that do not. Always check your local and state laws before purchasing or using a suppressor. Additionally, you will need to file paperwork and pay a tax stamp fee to the ATF to purchase a suppressor.