A number of them have taken to Twitter to voice their concerns.
Grande suspended her tour in the wake of the bombing, and it seems some are hoping Bieber will follow her lead.
It's understandable why Grande made this decision, as she's just been through an extremely traumatic experience.
But Bieber actually has an opportunity to send a powerful message of defiance against terrorism by not canceling his tour.
The goal of terrorism is to spread fear in order to change a society's behavior.
Terrorists want people to become so afraid they fundamentally alter who they are and what they do.
By refusing to cancel his tour, Bieber would also be refusing to give the terrorists what they want.
In the process, he'd be setting an example for all of us.
The greatest victory we can win over terrorism is to live our lives exactly as they were before.
We have to refuse to give in to the fear the terrorists seek to instill within us.
It's completely understandable why people are afraid of terrorism, but we need to keep things in perspective.
Terrorist attacks are deeply frightening and disturbing.
The truth is, however, terrorism poses a very small threat to people in Western societies.
In the U.S., for example, jihadists have killed 95 people since 9/11, according to New America.
While this certainly tragic and we should mourn the loss of any innocent life, this number pales in comparison to other causes of death in the U.S.
Gun violence, for example, claims well over 10,000 lives in the U.S. every single year.
Americans are more likely to be killed by a lightning strike than a terror attack.
This is precisely what makes terrorism so terrifying: It's rare. It's not a normal part of our lives.
There's a strong psychological aspect to why people in Western societies are so afraid of terrorism in spite of this fact.
The primary victims of jihadism are Muslims in majority Muslim countries. Even President Donald Trump, who doesn't have the most tolerant disposition toward Islam, acknowledged this in a recent speech in Saudi Arabia.
But the actions countries like the U.S. and the UK have taken to combat terrorism in the post-9/11 era arguably don't reflect the reality.
In other words, there's a strong case to be made the U.S., in particular, has offered a disproportionate response to terrorism in relation to the threat it poses to American lives.
The true danger of terrorism is not the attack itself, but how we respond.
Terrorism is designed to provoke a response.
Terrorists know attacks like the one at the Manchester arena -- or even 9/11 -- however tragic and heartbreaking, are not capable of completely destroying our societies.
What they hope is that we will overreact, embrace fear and make choices that erode our most cherished values.
Many experts feel the U.S. has played into the terrorist's hands with its response to terror attacks and has found itself bogged down in an un-winnable conflict as a consequence.
Nearly 16 years after 9/11, for example, the U.S. military is still involved in Afghanistan and Iraq, and it now finds itself mixed up in the conflict in Syria, as well as parts of Africa, in its efforts to thwart terrorism.
All of these actions are not only unethical, but help groups like ISIS demonize America and gain new recruits.
America has learned the hard way that overreacting to terrorism grants terrorists a bigger victory than any attack ever could.
It might sound ridiculous, but Bieber actually has an opportunity to remind us this is the wrong route to take in the aftermath of terror attacks.
We can't let terrorism take the joy out of life.
The senseless attack in Manchester was at a concert for young people, which is Bieber's fan demographic as well.
It's clear the terrorists wanted to send a message that no one is safe -- not even children.
They want to suck the joy out of life.
This is precisely why Bieber shouldn't cancel his tour.
We shouldn't be afraid to go outside (or to our favorite musician's concert).
Our governments should not respond to terror attacks with expensive, counterproductive military operations.
People should not blame the world's 1.7 billion Muslims for the actions of a few.
There are certainly measures we should take to protect ourselves and our societies from terrorism, but this shouldn't come at the cost of removing enjoyment from life or violating our core beliefs.