To check this, go the Windows 95 Troubleshooting Guide . When you kill it in the task list, everything is OK again. You might have wondered what in the world Rnaapp.exe is, as you did not start it yourself.
Nobody knows, at least nobody wants to tell.
Fortunately, there is a procedure that might solve the problem for you. Download the ISDN Acellerator Pack 1.1 from Microsoft. Don't worry about the name, you can install it if you are using a modem or ISDN hardware without drivers for it. Simply ignore the ISDN-only files it installs. The point is that it includes updates to many components of Dial-Up Networking, including Rnaapp.exe.