Anjem Choudary was remanded in custody until 28 August.
Both men have each been charged with one offence under section 12 of the Terrorism Act 2000, alleged to have taken place between 29 June 2014 and 6 March this year.
The BBC's Simon Jones, reporting from outside the court, said that when asked by the judge to give an indication of how he would be pleading Choudary said: "Cameron and the police are guilty."
The judge replied to say he took that to mean he would be pleading not guilty.
Mr Choudary 48, was described in court as a "high-profile figure" in the media and on social media.
The court also heard that the charge is related to him sending messages to his 32,000 followers on Facebook.
Mr Choudary, of Ilford in east London, and Mohammed Rahman, 32, of Whitechapel in east London, were arrested on 25 September last year on suspicion of being members of IS, which is a proscribed organisation.
Proscription means membership of the militant group is a criminal offence, and that the organisation cannot lawfully operate in the UK.
Sue Hemming, of the Crown Prosecution Service, said: "It is alleged that Anjem Choudary and Mohammed Rahman invited support for Isis [also known as IS] in individual lectures which were subsequently published online."
Mr Choudary is the former UK head of Islamist group al-Muhajiroun - also known as Islam4UK - which was banned in 2010.
The former lawyer planned an Islam4UK march through Wootton Bassett, Wiltshire, to honour Muslims killed in the Afghanistan conflict, but those plans were later scrapped.'
The town is where repatriated bodies of dead UK soldiers were driven through the streets from nearby RAF Lyneham.
Ofcom launched an investigation into interviews broadcast on BBC, ITV and Channel 4 with Mr Choudary in the days following the murder of Fusilier Lee Rigby.