noun which may take the genitive case particle 'no'
civil; in civil matters
Used in legal contexts to refer to civil (as opposed to criminal) matters. Typically modifies a noun with の.
民事上の責任を問われる可能性がある。
There is a possibility of being held civilly liable.
これは民事上の問題であって、刑事事件ではない。
This is a civil matter, not a criminal case.
民事 is a noun meaning 'civil affairs'; 民事上 is the adjectival form used before nouns.
Compound of 民事 (civil affairs) + 上 (suffix meaning 'from the standpoint of' or 'regarding').