Seven Northern Virginia schools received bomb threats by robocall about midday Friday, law enforcement officials said.

Authorities are investigating whether the threats to the following schools are connected to threats to schools in New Jersey Friday:

Bishop O'Connell High School in Arlington

George Mason High School in Falls Church

Herndon High School in Herndon

McLean High School in McLean

Stone Bridge High School in Ashburn

The Potomac School in McLean

Westfield High School in Chantilly

Bishop O'Connell, Stone Bridge and George Mason were evacuated. Authorities later gave the all-clear at those schools.

Police checked all the schools and found nothing.

"Police are investigating and have determined the threats are not credible, and are intended only to disrupt school operations," Fairfax County Public Schools (FCPS) said in a statement. "We do not believe any FCPS students are at risk and we are continuing with normal school operations at all of our schools for the remainder of the day."

The Potomac School, a private school in McLean, said it received a bomb threat at 11:30 a.m. Friday. School officials said the recorded message it received was brief and non-specific. The school did not evacuate based on recommendations from police and the number of threats received by other schools.

Students at Westfield, McLean and Herndon also went about regular day while authorities scoured the buildings.

Loudoun County school officials said students from Stone Bridge High School were sent to Riverside High School while four police dogs searched the school. After about two hours, police said the school was clear, the sheriff's office said. Students returned to their classes about 1:30 p.m., Principal Matt Wilburn posted on Twitter. Dismissal will happen at the school's regular time, Wilburn said.

George Mason was evacuated, sending students to the nearby Mary Ellen Henderson Middle School at about 11:40 a.m. Falls Church schools officials were asking parents not to pick up their children. Students spent the rest of the day in the gym at the middle school.

Some George Mason students told News4 they were annoyed by the inconvenience, but they said very few were fearful.

"I knew it was fake," student Joseph Stokes said.

Students from Bishop O'Connell, a Catholic school in Arlington, waited in the libary at Tuckahoe Elementary School as police K9s searched their school. They returned to classes about 1:50 p.m.

Earlier this week, students at McLean High School were sent home early after the school received a bomb threat.

School safety experts say bomb threats are becoming a disturbing trend throughout the country.

"Unfortunately, it's pretty much business as usual. That's what we've been seeing almost every school day this whole academic year. We're averaging nationally somewhere between eight to ten bomb threats a day," said Dr. Amy Klinger with the Educators Schools Safety Network.

Klinger specializes in school safety training and told News4's Shomari Stone the schools can't take any chances.

"We look at threats and think oh, okay well maybe nothing's probably going to happen. But the problem is schools are really in this dilemma of you have to do something. We can't ignore it. But yet, we're continually evacuating and so it really becomes a frustrating experience for schools."

1/2 Several bomb threats received in Fairfax County and throughout the region. All appear to be non-credible at this time. — Fairfax County Police (@FairfaxCountyPD) March 4, 2016

Editor's Note: This article has been corrected from a previous version.