To clarify, the passive voice is used when the subject of the sentence is the recipient of the action, rather than the performer of the action. In this sentence, "me" is the recipient of the action of being kept.
To make it active voice, you would need to know who or what is doing the keeping. For example:
* Active voice: "The dog kept me."
* Active voice: "My parents kept me."
Let me know if you have another sentence you'd like to see in passive voice!