It deprnds on the situation.
To start conversation, I would use:
(name)さんはコンピューターに興味がありますか。
After talking about computer, for example, she/he knows very well about it or she/he seem to be interestet in it, to make it clear or when I'm a bit surprised, I would ask:
(name)さんはコンピューターに興味があるんですか。
I hope this helps you.