diff --git a/.changeset/cool-cups-dig.md b/.changeset/cool-cups-dig.md
new file mode 100644
index 0000000000..4b4b7693c9
--- /dev/null
+++ b/.changeset/cool-cups-dig.md
@@ -0,0 +1,5 @@
+---
+"better-auth": patch
+---
+
+The admin plugin's `unbanUser`, `setRole` and `adminUpdateUser` endpoints used to call `internalAdapter.updateUser` without checking that the target user existed, so when the caller passed an unknown id the underlying database error (for example Prisma's `P2025`) bubbled up as a generic HTTP 500. those endpoints now mirror the existing guard in `banUser`: look the user up via `findUserById`, and throw a clean `NOT_FOUND` (`USER_NOT_FOUND`) when no row is returned. Closes #9800.
diff --git a/packages/better-auth/src/plugins/admin/admin.test.ts b/packages/better-auth/src/plugins/admin/admin.test.ts
index 16a0ec75f2..5bc8fd969d 100644
--- a/packages/better-auth/src/plugins/admin/admin.test.ts
+++ b/packages/better-auth/src/plugins/admin/admin.test.ts
@@ -719,6 +719,62 @@ describe("Admin plugin", async () => {
 		expect(res.data?.sessions.length).toBe(1);
 	});
 
+	it("should return 404 from unbanUser when the target user does not exist", async () => {
+		const res = await client.admin.unbanUser(
+			{
+				userId: "nonexistent-user-id",
+			},
+			{
+				headers: adminHeaders,
+			},
+		);
+		expect(res.error?.status).toBe(404);
+		expect(res.error?.code).toBe("USER_NOT_FOUND");
+	});
+
+	it("should return 404 from banUser when the target user does not exist", async () => {
+		const res = await client.admin.banUser(
+			{
+				userId: "nonexistent-user-id",
+			},
+			{
+				headers: adminHeaders,
+			},
+		);
+		expect(res.error?.status).toBe(404);
+		expect(res.error?.code).toBe("USER_NOT_FOUND");
+	});
+
+	it("should return 404 from setRole when the target user does not exist", async () => {
+		const res = await client.admin.setRole(
+			{
+				userId: "nonexistent-user-id",
+				role: "admin",
+			},
+			{
+				headers: adminHeaders,
+			},
+		);
+		expect(res.error?.status).toBe(404);
+		expect(res.error?.code).toBe("USER_NOT_FOUND");
+	});
+
+	it("should return 404 from admin.updateUser when the target user does not exist", async () => {
+		const res = await client.admin.updateUser(
+			{
+				userId: "nonexistent-user-id",
+				data: {
+					name: "John Doe",
+				},
+			},
+			{
+				headers: adminHeaders,
+			},
+		);
+		expect(res.error?.status).toBe(404);
+		expect(res.error?.code).toBe("USER_NOT_FOUND");
+	});
+
 	it("should not allow non-admin to list user sessions", async () => {
 		const res = await client.admin.listUserSessions(
 			{
diff --git a/packages/better-auth/src/plugins/admin/routes.ts b/packages/better-auth/src/plugins/admin/routes.ts
index f79986fe27..e26b13b87d 100644
--- a/packages/better-auth/src/plugins/admin/routes.ts
+++ b/packages/better-auth/src/plugins/admin/routes.ts
@@ -153,6 +153,14 @@ export const setRole = <O extends AdminOptions>(opts: O) =>
 					}
 				}
 			}
+
+			const isUserExist = await ctx.context.internalAdapter.findUserById(
+				ctx.body.userId,
+			);
+			if (!isUserExist) {
+				throw APIError.from("NOT_FOUND", BASE_ERROR_CODES.USER_NOT_FOUND);
+			}
+
 			const updatedUser = await ctx.context.internalAdapter.updateUser(
 				ctx.body.userId,
 				{
@@ -507,6 +515,14 @@ export const adminUpdateUser = (opts: AdminOptions) =>
 					inputRoles as string[],
 				);
 			}
+
+			const isUserExist = await ctx.context.internalAdapter.findUserById(
+				ctx.body.userId,
+			);
+			if (!isUserExist) {
+				throw APIError.from("NOT_FOUND", BASE_ERROR_CODES.USER_NOT_FOUND);
+			}
+
 			const updatedUser = await ctx.context.internalAdapter.updateUser(
 				ctx.body.userId,
 				ctx.body.data,
@@ -851,6 +867,13 @@ export const unbanUser = (opts: AdminOptions) =>
 				);
 			}
 
+			const isUserExist = await ctx.context.internalAdapter.findUserById(
+				ctx.body.userId,
+			);
+			if (!isUserExist) {
+				throw APIError.from("NOT_FOUND", BASE_ERROR_CODES.USER_NOT_FOUND);
+			}
+
 			const user = await ctx.context.internalAdapter.updateUser(
 				ctx.body.userId,
 				{