It is always best to keep all nuts, including cashews, out of reach of your dog. If your dog does happen to eat a few cashews, they are not likely to cause serious harm, but it is still a good idea to monitor them for any signs of digestive upset and to contact your veterinarian if you have any concerns.
As a general rule, it is best to stick to feeding your dog a diet that is specifically designed for their nutritional needs, rather than giving them human foods as treats. This will help ensure that they are getting all of the nutrients they need to stay healthy. If you want to give your dog a treat, there are many dog-safe options available, such as small pieces of cooked, unseasoned meat or vegetables.