Engelli Web reported on Sunday that the "NatoDefol" (NATO out) website had been blocked by court order on national security and public order grounds.
An online petition with the name "Nato'ya Hayir" (No to NATO) has also been blocked, according to Engelli Web, and the campaign website could not be accessed in Turkey.
Engelli Web reported on Saturday that an article in the progressive Sol newspaper had been blocked by court order.
The article said that urgent repair work to roads had been initiated only for the summit.
However, the article remained accessible in Turkey.
The government has repeatedly tightened laws on the regulation of social media and websites over recent years.
Ankara residents will be subject to restrictions during the summit on July 7-8, with concerts and other events banned and exams postponed.
According to media reports, police have instructed municipal authorities to impound stray dogs under a heavily criticised law.
The Cumhuriyet newspaper has reported that housefronts along the road from the city's new airport have been repainted.
President Recep Tayyip Erdogan opened the airport, previously used only by the military, to civilian traffic a week ago.
Turkey's state news agency Anadolu reports that 40,000 police and security officers will guard the summit.
