The lawyer, who was identified as Jaya Vindyala, has been sent to judicial custody for 14 days. The advocate, a member of the PUCL, was arrested from Prakasam district of the state.
The Congress MLA filed a complaint against the advocate on April 18 claiming Vindyala allegedly insulted him calling Mohan a "'paedophile.
The woman lawyer also has been accused of hurling allegations against the Congress MLA regarding a land mafia case in association with Rosaiah.
Andhra Pradesh police arrested her under Section 66A of the IT Act for posting defamatory comment on the social networking site. The Congress MLA also accused the PUCL of trying to dig out dirt against him through their fact finding teams.