No you can't because Entity Framework needs to know the key to keep track on the object when you make an update or delete operation.
Anyway it's not a good idea to have a table without a PrimaryKey
There is a great difference between what EF can do with a database, and what is possible with a database.
Most databases allow for a table to be without a primary key. Most databases also allow for a table to be without a clustered index / Index Organized Table (or what ever it is the specific term for it in other database systems).
There is nothing wrong with that, and one should not state that it is a bad idea to have a table without a PK.
As always, it dependes on the needs and usage of the specific table. e.g. a log table, does not need a PK. It will never be used as a FK, so what is it use?
Bottom line, EF does not support tables without a key out of the box, there are some weird workarounds, but none that I have seen is good enough. That is a shame.