What does he mean when he says "I'm keeping tabs on you"?

My guy friend won't ask me out but he always wants to know who I am with and where I am at. I called him up one night and he said "Where are you going?" I said "Why?" He said "I'm keeping tabs on you" He said it real seriously. I just want to know what that exactly means? If it's alarming or not...ty!
What does he mean when he says "I'm keeping tabs on you"?
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