The active voice is formed by putting the subject of the passive sentence before the verb and the past participle of the main verb. In this case, the subject of the passive sentence is "I" and the main verb is "ridicule." The past participle of "ridicule" is "ridiculed." So, the active form of the sentence is I was not ridiculing anybody.

The other options are incorrect because:

• I did not ridicule anybody is in the simple past tense, while the original sentence is in the present progressive tense.
• I were not ridiculing nobody is grammatically incorrect. The verb "to ridicule" is followed by a direct object, but the phrase "were not ridiculing nobody" is not a direct object.
• I am not ridiculing anybody is in the present tense, while the original sentence is in the present progressive tense.