Yes.
My son learns his math on a computer, in fact -- the Stanford Math Program.
Young kids need adult supervision and interaction with computers. Like anything (including outside play), moderation is key. Nothing is a substitute for anything else, but there are some things computers allow kids to do that they can't do elsewhere (anyone ever play Incredible Machine?).
A computer is a tool. It can be misused like anything else. It's up to the parents to make sure.
And I would suspect that too much television would have a much greater impact than too much computers.
Now, some caveats: my son is home schooled, and he's not allowed to play computer games. So keep that in mind when addressing the above comments. :-)
