negating

"Indeliberate" is correct, though rather antiquated and unnatural-sounding. You may want to choose a replacement word, such as: "accidental," "random," or "unplanned.

Depending on the context, you might want to use non-deliberate; if it were a formal context, for example.

Armchair Linguist: http://comfylinguist.blogspot.com/

Oops, I see you don't support HTML. Sorry. :)

Deliberate is one of those fun English words that has two very different meanings, yet appears the same in both.

To "deliber-ATE", means: to discuss, debate, argue, etc. an issue or topic.

"They were in deliberations for hours."
"They deliberated about whether it was better to go with red than with blue."

For this meaning/pronunciation, the opposite meaning would thus be to "agree", "concur", or
"compromise".
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To do something "deliberately" or to be "deliberate" with a short 'ate' instead of a long---means: to do something willfully, with intention, on purpose.

"He deliberately ate my food in retaliation for me stealing his shampoo."

The opposite of this would thus be
"unintentional", "not on purpose", "I didn't do it deliberately!", etc.

try 'inadvertent'.