It doesn't work that way. However, you can run:
ls | grep -v \.html\$
and get the answer you are looking for.
This will send the ls output to the grep command. The parameters for grep tell grep to return all lines that do not (the -v) end (the $) with ".html". the "." and the "$" must be escaped so the shell doesn't try to expand them before they are send to the grep command.